Diagnosis and treatment
of benign nail tumours
Dermatology Practice, Freiburg, Germany
Department of Dermatology, St Radboud University, Nijmegen,
Department of Dermatology, Inselspital, Berne, Switzerland
The tip of the finger and toe form a functional unit with the nail organ. Tumours of this particular region will therefore influence the shape, size and quality of the nail and the entire distal phalanx and also exert profound effects on the sensory function of the finger tip, the mobility of the finger and even the hand or foot as a whole. Since the distal phalanx is made up of many different tissue structures, a great variety of tumours may be observed, even those that usually do not come to the attention of the dermatologist. On the other hand, nail-specific tumours are rare, in contrast to neoplasms originating from the hair follicle.
This article will give a brief overview of the most important tumours of the distal phalanx and their treatment and prognosis.
Key words: Benign nail tumours, diagnosis, therapy, prognosis, melanonychia longitudinalis.
In the distal phalanx, almost
all skin tumours except those of the hair follicle may occur. In addition, the
bone of the terminal phalanx, cartilage, tendon sheath, blood and lymph vessels
as well as nerves may give rise to true tumours and reactive tumour-like lesions.
However, tumours comparable to those of the follicle but originating from the
nail matrix are very rare1.
Nail tumours are often difficult to diagnose, because the particular anatomical conditions, specifically in subungual tumours, lead to a different growth pattern and often to also different symptomatology. For instance, pain is a characteristic symptom of fast-growing lesions, but may suggest a traumatic origin even though this was not the cause. All changes hidden under the nail plate or proximal nail fold should prompt a radiological examination. Xeroradiography is particularly useful, as it avoids overexposure of the terminal phalanx, gives magnification and often also allows evaluating the nail plate and soft tissues surrounding the nail. A dental radiograph is an alternative, as this technique is specific for the demonstration of small bony structures. Probing localises areas of most intense pain, e.g. in subungual felon or glomus tumours, but also allows the extent of an onycholysis to be evaluated. Transillumination, also termed diaphanoscopy, gives information about potential cystic lesions and sometimes about a foreign body, as it may give a sharply delimited shadow. Examination of the nail region should be done with the fingers or toes in relaxed position, in extreme flexion and extension, as well as with pressure of the digital tip on a hard surface, as this allows evaluating the blood circulation. Dermatoscopy allows differentiating melanin from haemoglobin and other pigments, it is almost as precise as capillary microscopy and permits the visualisation of subungual foreign bodies and infestations with scabies mites. Magnetic resonance imaging is useful for the diagnosis of deep-seated lesions, particularly for subungual glomus tumours and submatrical myxoid pseudocysts. High-resolution ultrasound may be used to measure nail plate thickness.
The hand is one of the most cosmetically important regions, following the face and the female breast. An intact and beautiful nail is of utmost importance for the hand's look. However, the nail has more functions, such as those of a mechanical tool and part of the sensory organ "fingertip". All surgical interventions have to respect these particularities and require surgical skills, in addition to a sterile operation theatre and fine instruments for atraumatic surgery.
Benign and self-limited lesions, such as viral warts, must not be treated with a technique leaving unsightly scars or a postoperative nail dystrophy. Recurrence after removal of a benign tumour, such as a subungual keratoacanthoma, synovialoma or recurrent infantile fibromatosis, should never be treated with amputation of the digit.
Pre- and postoperative care has to be explained to the patient. Smoking is forbidden until wound healing is complete. Antibiotic prophylaxis is considered beforehand, particularly in case of ulcerated or infected lesions. An efficient tourniquet is used to achieve a completely bloodless field whenever necessary. The tourniquet is opened after 15-20 min to allow blood supply for approximately 3 min, and then re-applied. Atraumatic surgery, fine instruments and a head magnifier lens or surgical microscope are prerequisites for good nail surgery. Whenever possible, the nail plate should remain in place or be replaced after surgery of benign lesions, as this represents the best physiological dressing. It can be fixed with mattress sutures and guarantees a much faster healing with fewer complications.
and pseudotumours Viral warts
Subungual and periungual warts are by far the most common tumour-like alterations of the nail regions. They are mainly seen in children and adolescents. If warty lesions develop in persons over 35 to 40 years and do not respond to wart treatment, Bowen's disease should be considered for differential diagnosis. Warts are hard, rough-surfaced, greyish, hyperkeratotic papules that often contain tiny black dots corresponding to the histological phenomenon of thromboses in the tip of the dilated capillaries. Whereas being round on the pulp of the digit the warts are often oval or even crescentic and less hyperkeratotic on the proximal nail fold or hyponychium. Deep fissures may cause pain. Subungual warts may even erode the underlying bone2. Most commonly, human papillomavirus types 1, 2, and 4 as well as 7 in butchers are found.
The differential diagnosis is important as in adults Bowen's disease may mimic viral warts. Other diseases to be ruled out are subungual exostosis and other tumours, tuberculosis cutis verrucosa etc.
Warts on the distal phalanx may be extremely recalcitrant. A surgical treatment is however rarely indicated, since it not only will leave scars and sometimes irreversible postoperative nail dystrophy, but its recurrence rate is as high as that of conservative therapies. In situ hybridisation has shown that HPV DNA may be found up to 15 mm around the wart.
We prefer an aggressive conservative approach with saturated monochloroacetic acid (Acetokaustin in Germany). The solution is sparingly applied on the wart, left to dry and then covered with 40 to 60% salicylic plaster (Guttaplast), which is fixed with adhesive tape for a week. During this time, the patient has to apply hot finger or footbaths twice daily, while leaving the salicylic plaster on to stimulate the blood circulation; smoking should be interdicted. After a week, the salicylic acid plaster is removed after another hot bath and the necrotised keratin masses are gently removed with a curette. This procedure is repeated until the warts are completely gone. This treatment is also applicable in little children. Imiquimod after keratolysis and under occlusion is a new alternative. Intralesional bleomycin injection may be very painful. The carbon dioxide laser as well as curettage with a curette or ring scalpel require local anaesthesia. In our hands, vascular lasers that are thought to dry out the warts by coagulating its blood vessels do not work. Suggestive therapy is rarely effective in this localisation. Wart treatment always takes much more time in smokers than in non-smokers.
Figure 1. Epiungual fibrokeratoma a. before surgery.
b. The origin of the lesion is visualised after opening the nail pocket.
Figure 2. Intraungual fibrokeratoma partly covered by a nail plate lamella.
Figure 3. Koenen tumours of tuberous sclerosis (Bourneville-Pringle disease): a. multiple ungual fibromas of the 3rd toe, b. resection of the fibromas en bloc.
Figure 4. Eruptive angioma (so-called pyogenic granuloma), a. before surgery, b. 10 days after excision and closure of the primary defect with two flaps from the adjacent skin of the proximal nail fold, c. 6 months after surgery, almost no scar is visible and the nail plate is growing out completely normal; note the longitudinal depression in the distal half of the nail plate from the pressure of the erauptive angioma on the matrix.
Of the many different cysts seen in the skin, only traumatic epidermal and postoperative matrix cysts are seen in the distal phalanx.
Epidermal cysts usually present as slow growing space occupying process. Depending on their location within the nail organ they may cause nail clubbing with increase in nail size or bone erosion with an eventual fracture. Matrix cysts preferentially develop after operations at the lateral matrix horn when matrix epithelium was left in place. Most commonly, a nail spicule develops, more rarely a cyst containing very hard keratin and the wall of which may histologically exhibit feature of both epidermis and matrix epithelium. In elderly persons, metastases and slow-growing osseous tumours have to be ruled out differential diagnostically. Complete extirpation is the treatment of choice. Either a lateral L-shaped or a longitudinal nail bed incision usually allows the lesion to be shelled out.
This nail-specific lesion was observed in the lateral nail groove and adjacent nail bed of elderly women. Clinically, an asymptomatic, markedly hyperkeratotic lesion was seen. Histopathology showed a crateriform tumour filled with keratin almost identical to the so-called trichilemmal horn. Clinically and histologically, keratoacanthoma is the most important differential diagnosis.
Complete excision resulted in permanent cure.
The onychomatricoma was described as an entity approximately 15 years ago. Its clinical appearance is so characteristic that it can be diagnosed on clinical grounds alone in most cases. There is a limited longitudinal thickening of the nail with yellow discoloration and tiny splinter haemorrhages, and transverse overcurvature. At the free nail margin, minute holes may be seen. After avulsion of the nail, a villous tumour of the matrix is seen. The corresponding nail plate shows holes into which the finger-like projections of the matrix tumours fit. Longitudinal sections of the nail show canals in the nail substance that are lined by matrix epithelium and extend distally to the free nail margin. Total excision will lead to permanent cure, though there will be a postoperative defect of nail growth depending on the size of the surgical specimen[1,5,6].
The subungual localisation of keratoacanthoma is infrequent. In most cases, it originates at the hyponychium, less frequently in the lateral groove, exceptionally in the nail bed. Clinically, it is a rapidly growing tumour soon reaching the underlying bone. Pain is characteristic. The clinical diagnosis may be difficult when the nail plate covers the lesion. Cutting away the overlying nail will reveal a tumour with a central horn plug. This is sometimes expressed during surgery. Histopathology reveals a vertically oriented, keratin-filled tumour that often reaches the bone and erodes it. Differential diagnostically, trauma, foreign body, subungual warts and other tumours, particularly the non-tender squamous cell carcinoma, have to be considered.
The excision has to reach down to the bone, maybe even include a lamella of bone to avoid a recurrence. Mobilisation of the wound margins usually allows the wound to be closed primarily. A small onycholytic area may be the only sequel.
Figure 5. Subungual glomus tumour of the ring finger causing a red stripe in the nail bed.
Figure 6. Recurrent myxoid pseudocyst after removal with CO2 laser a. before re-operation, b. end of surgery after raising a U-shaped flap, dissecting the degenrated myxoid connective tissue and suturing the flap back into its original position.
of the nail organ
Fibromas are relatively frequently located on the distal phalanx. They may be hereditary or acquired and differ in their histopathology[8,9]. Ungual fibromas cause variable nail changes depending on their origin within the nail apparatus. A deep canaliform depression is typical for those coming from the proximal matrix, whereas nail bed fibromas cause a rim in the nail.
Ungual fibrokeratomas are the most frequent variety. Most of them come out from under the proximal nail fold and cause a longitudinal depression. When their origin is in the central matrix area, they run within the nail plate until the overlying nail lamella breaks off showing the tip of the sausage-like tumour (figure 1). Their distal end may be split into several free ends. The differential diagnosis of early lesions is verruca vulgaris; long-standing lesions may resemble a foreign body or a myxoid pseudocyst that penetrated through the proximal nail fold's undersurface into the nail pocket.
The treatment of choice is its excision down to the bone in order to avoid a recurrence. Fibrokeratomas lying on the nail plate (epiungual fibrokeratomas) (figure 2) are excised with a Νο11 scalpel blade, which is held parallel to the nail plate surface, thus permitting to incise around the base of the fibrokeratoma, which is eventually severed from the bone with pointed curved scissors. The same approach is used for intraungual fibrokeratomas; however, the overlying nail plate lamella has to be removed before. The small defect does not require a suture.
Subungual fibrokeratomas are excised from the distal matrix/nail bed accordingly. A 6-0 PDS suture is recommended to close the small defect.
Koenen's tumours are a characteristic sign of tuberous sclerosis. From the age of 10 to 12 years, they develop in approximately half of the patients. They always occur in multitude and may destroy the entire nail organ if treatment is delayed. Though most of them develop in the proximal and lateral grooves, they may completely occupy the matrix and nail bed. They are excised at their base without wound suture (figure 3). The cosmetic result depends on how much healthy the nail tissue is[8-10].
This rarely described lesion is certainly underdiagnosed. It usually presents as a narrow whitish to yellowish, sometimes even brownish longitudinal stripe in the nail that often causes nail splitting at its free margin. Clinical examination reveals a small rim of keratin at the undersurface of the nail that may be pared down painlessly. In case treatment is requested the nail plate is cut longitudinally at both sides of the streak and elevated. The beginning of the lesion is seen at the nail plate's underside in the distal lunula part and in the distal matrix region as a tiny spike of tissue. This is removed by a saucer-shaped small excision, which does not require a suture. However, recurrences are not uncommon.
Figure 7. Longitudinal melanonychia due to a junctional naevus of the nail matrix.
Granuloma pyogenicum is not a granuloma, but an eruptive angioma. When occurring in the nail region, it is mainly seen on the nail fold or hyponychium. A pyogenic granuloma penetrating the nail plate is commonly due to a perforating trauma. The differential diagnosis of multiple pyogenic granulomas, coccal nail fold angiomatosis, and granulation tissue is often very difficult, but other erosive tumours including amelanotic melanoma and squamous cell carcinoma have to be taken into consideration. Granulation tissue may also develop under treatment with retinoids, some systemic antivirals, taxane type cytotoxic drugs[11-16].
Treatment of choice is its excision at the base and gentle electrocoagulation of the central feeding artery. When located at the free margin of the proximal nail fold, it should rather be excised with a wedge shaped nail fold excision. The defect is closed after separation of the proximal nail fold from the underlying nail plate, longitudinal incisions at both sides and suture of the central defect (figure 4). This leaves to narrow secondary defects, which rapidly heal without a visible scar. Angiomas of the matrix and nail bed are removed by horizontal excision and ligation of the feeder vessel. Electrocoagulation has to be kept to a minimum in order to avoid scarring and postoperative nail dystrophy.
The subungual glomus tumour is undoubtedly the best known of all nail tumours, even though it is by far not the commonest. Its clinical symptomatology is so characteristic that it is correctly diagnosed in most cases. However, patient histories of decade-long suffering are known. The patients have increasing pain in the distal phalanx exacerbating after minor shock or cold temperature and radiating to the shoulder. Applying a finger tourniquet or a blood pressure manchette pumped up to >200 mmHg makes the pain almost immediately disappear. Clinically, a livid-red spot in the matrix or nail bed is seen, from which a reddish stripe extends to the hyponychium (figure 5). The exact localisation is found using a blunt probe: the point of most intense pain corresponds to the glomus tumour. MRI is also useful to localise the lesion.
All painful lesions or those tender on touch or palpation have to be considered in the differential diagnosis (table 1).
Glomus tumours in the lateral third of matrix or nail bed are extirpation via a lateral L-shaped incision permitting the nail bed and matrix to be dissected from the bone. The glomus tumour is seen as a greyish glassy round tumour, about the size of a peppercorn or a pea[8,10,17]. Tumours in median position in the matrix require avulsion of the overlying nail plate, either as a disc of nail punched out with a 6mm diameter punch, or by incising the nail plate from its lateral margin and detaching it from the nail bed in a trap-door manner. The tumour is seen as a violet spot. The incision is performed over the tumour, in transverse direction in the matrix, in longitudinal direction in the nail bed. The soft grey nodule is meticulously dissected and shelled out. The defect is sutured with 6-0 PDS stitches and the nail plate laid back. The pain disappears within 2 to 3 days. Wound healing is complete within 8 to 14 days, since the replace nail plate considerably improves healing. Primary multiple or successive glomus tumours may be the cause of persisting pain and may suggest recurrence.
Neurogenic tumours of the distal digit are rare. Sometimes, a traumatic or amputation neuroma develops after injury; however, there is no characteristic clinical (table 1). Neurofibromas are very rare and almost always singular. Even in neurofibromatosis von Recklinghausen with thousands of tumours on the rest of the body, ungual neurofibromas are exceptional. Neurilemmomas, which are even less common than neurofibromas, may be seen in the palmar side of the distal digit and cause grotesque swelling. The treatment of choice is complete extirpation. The surgical technique depends on the localisation within the nail apparatus or distal phalanx.
Synovialomas sometimes develop in the distal phalanx. Dorsally located ones form irregularly sized nodes that may resemble Heberden nodes. They may exert pressure on the matrix, thus interfering with nail growth. They have to be excised generously in order to avoid a recurrence. For precise dissection, a head magnifier lens is required. Defect closure is achieved with a full-thickness skin graft. Synovialomas in the pulp of the digit cause a considerable swelling of both the pulp and the nail. The skin is opened with an L-shaped incision at the lateral aspect of the distal phalanx and the yellowish-brown, corym-biform tumour is completely extirpated. This is done by blunt dissection, as it has a fibrous capsule in this localisation in contrast to synovialomas in dorsal position. The histopathology shows a cellular tumour made up of histiocytes, fibroblast, some foam cells, siderophages and characteristic osteoclast-like giant cells. Minute calcifications seen on X-ray film are said to be a sign of malignancy.
Subungual exostoses are reactive lesions most commonly provoked by chronic repetitive microtrauma. Their most common localisation is therefore the medio-dorsal aspect of the distal hallux phalanx. Most patients are young adults, however they are also seen in children and elderly persons. Bone fragments after fracture of the distal phalanx may mimic an exostosis8,19. Whether or not subungual osteochondromas represent a different entity is still under debate.
Clinically, most tumours are stone-hard nodes that elevate the nail plate. The overlying epidermis is often thin and has lost its dermatoglyphic pattern, but it may also be ulcerated. Confirmation of the diagnosis by radiograph is strongly recommended, as it also allows the extent of the lesion to be determined. The skin is incised and the bony lesion dissected. It is finally clipped off at its base using a bone rongeur or a strong nail clipper. The wound is closed with simple sutures.
The regrowing plate induces completely normal nail conditions. A final X-ray is useful to control the extent of exostosis removal. When the exostosis is under the nail the incision has to be adapted accordingly[10,21].
This lesion is also called dorsal finger cyst. It is a relatively frequent degenerative lesion occurring mainly in the second half of life. More than 90% are located on the fingers, less than 10% on the toes. Women are more frequently affected. An associated degenerative osteoarthritis of the distal interphalangeal joint, often with Heberden nodes, is seen in most cases and probably of aetiological significance. Clinically, a round, slightly dome-shaped, skin coloured to greyish-glassy, soft to elastic tumour is seen in the proximal nail fold. Its pressure on the matrix causes a longitudinal depression in the nail[10,22]. On the toes, it is almost always a round transparent lesions bulging up, thus not causing a canaliform depression in the nail. Primary subungual location is possible and causes a rapidly developing limited overcurvature of the nail. The lunula takes on a characteristic violaceous colour. Diaphanoscopy helps in making the diagnosis.
A variety of different treatments were proposed: multiple puncture and expression, injection of steroid crystal suspension, of sclerosants, of hyaluronidase, cauterisation, CO2-laser vaporisation, cryosurgery, simple excision and even amputation. We have combined the methods of Kleinert and Newmeyer[25,26]: a minute amount of sterile methylene blue (methyl thionine) is injected into the distal interphalangeal joint through the volar crease just next to the flexor tendon; this allows the true extent of the lesion to be seen. If the skin overlying the cystic lesion is not too thin, a U-shaped or triangular flap is incised over and around the lesion and raised. Since the lesion gains connection with the joint it will be stained blue, as also the surrounding myxoid tissue. This is meticulously dissected and the stalk to the joint is ligated using 6-0 PDS stitches.
Complete extirpation after previous demonstration of the lesion's extent with methylene blue is superior to all other techniques described in the literature. If the overlying skin is not too thin, a U-shaped incision around the distal 3/4 of the cyst is performed and the flap is cautiously dissected from distal to proximal and the underlying degenerated tissue is removed. Any connection with the distal interphalangeal joint -this is the case in more than 80%- will be visible by the blue staining of the myxoid tissue and the pseudocyst; the stalk to joint is seen as a dark blue spot. This is ligated with 6-0 PDS stitches. The flap is laid back and sutured again. If the skin overlying the lesion is very thin, it will be excised and a small rotation flap rose from the adjacent skin to cover the defect. The resultant secondary defect rapidly heals by second intention and the scar is soon almost invisible. Primary subungual myxoid pseudocysts are rare. They have to be removed via a transmatrical approach. The proximal nail fold is separated from the underlying nail, incised at both sides and reflected. The proximal part of the nail plate is detached from matrix and cut transversely for about 2/3 to 3/4 of its width, this part is then reflected like a trap door permitting access to the submatrical lesion. This is then dissected and removed. The matrix incision is stitched with absorbable 6-0 PDS sutures. A completely normal nail will regrow[8,22]. It is important to apply the postoperative bandage in physiological flexion of the finger as joint stiffness is the most common complication.
alterations and brown nail pigmentations
Ungual melanoma is the most frequent and most serious malignant tumour of the nail apparatus. About 65-75% of them are pigmented and usually give rise to a longitudinal brown streak in the nail. This is why each acquired melanonychia in fair-skinned adults has to be examined and considered potentially malignant until otherwise confirmed[28-30]. Since there is no clear-cut clinical difference between nail pigmentation due to a melanoma or to a benign melanocytic lesion, their differentiation with any possible means is of utmost importance.
and black pigments
Brown and black nail pigmentation is usually due to melanin, microbial pigments, subungual or deeply intraungual blood, or exogenous substances, such as silver nitrate. Often the nature of the pigment can be suggested on clinical grounds and histology and/or biochemistry can confirm this assumption. For histopathology or histochemistry, the free margin of the nail plate is useful when the pigmentation involves it. Subungual keratosis is examined when it contains pigment. Superficial pigmentations may be diagnosed from a tangentially excised piece or a punched-out disc of nail.
Blood is the commonest cause or dark nail colorations. A single, almost always very painful trauma (see table 1), for instance due to a hammer blow or crush in a door, is remembered by the patient and is no diagnostic challenge. Just over the haematoma, a small leukonychotic area is often seen as a sign of the injury to the fibrous keratin structure of the nail plate. The matrix and/or nail bed tissue disrupts from the power of the trauma and blood gets under the nail plate. Any haematoma occupying more than half of the nail area is suspicious of a fracture of the terminal phalanx and should prompt an X-ray. Any bone dislocation has to be corrected to avoid later nail dystrophy. The pain after an acute trauma rapidly disappears when a small hole is drilled over the haematoma to allow it to be evacuated. Diagnostic problems may however arise in subungual haematomas of the great toe, particularly in lateral position, since their development is usually overlooked because the chronic microtrauma was not noticed. Hiking, skiing and other sports are the most common cause. An important differential diagnostic sign is that these haematomas do not reach the free margin of the nail and have an oval shape in contrast to melanocyte-derived longitudinal melanonychia. The dried blood under the nail usually grows out, but in rare cases it may be non-migratory. A small hole may then be punched into the nail and some of the pigment scraped out. This is collected in a small test tube, some drops of water are added, mixed, and with a haemostix such as is used to search for blood in urine, the true nature of the pigment can be revealed. The subungual blood pigment remains Prussian-blue negative, as it is not degraded to haemosiderin; this test is however extremely sensitive and will react to the smallest amount of blood that may come from injuring the nail bed during collection of the material. In addition, all bleeding tumours are also positive.
Microbial pigments are chemically different. Various pathogenic and harmless fungi produce melanin as resistance and virulence factors, e.g. in onychomycosis nigricans. The fungal melanin is soluble and not particulate, it therefore remains negative with the argentaffin reaction of Fontana-Masson. In a pale haematoxylin-eosin or PAS stain, this melanin appears as a diffuse yellowish colour of the nail. Heavily pigmented fungi may stand out by their dark colour. In most cases, both nail plate and subungual keratin can be clipped and used for histopathological and mycological examinations. Clinically, a dark spike is seen with its broad base at the distal margin of the nail plate, which rarely reaches to the matrix. Several black stripes or an extensive staining may occur in one nail. Trichophyton rubrum var. nigricans is the most common cause of fungal melanin. The commonest bacterial pathogens causing dark nail coloration are Pseudomonas aeruginosa, Klebsiella and Proteus spp. A greenish colour is in favour of Pseudomonas. Very often, the pigmentation is at the lateral margin of the nail plate, sometimes emerging from under the nail fold. In contrast to human melanin, it may be scraped off the surface, but soon recurs.
Exogenous pigment stains the surface and can often be scraped off or removed by tangential sectioning of the nail. It grows out with a proximal border parallel to the free margin of the proximal nail fold. Manganese dioxide, which develops from potassium permanganate used as a disinfectant, stains the nail and the surrounding skin. It can be removed with ascorbic acid wipes that reduce the dioxide to a colourless compound. Heavy smokers not only have a stained side of the nail, but also of the adjacent skin. Etching of granulations, for instance due to ingrowing nails, or of oozing tumours with silver nitrate stains the tissue jet-black including the nail plate. Black silver nitrate granules are seen in the upper layers of the nail plate in histological sections. The silver stain grows out with the nail.
Human melanin is finely granular, intracellular in the onychocytes and is argentaffin[10, 33]. Single pycnotic melanocytes in the nail plate are a sign of subungual melanoma that exhibits a pagetoid melanoma cell spread in the matrix epithelium leading to intraungual melanoma cells. The localisation of the melanin in the nail plate gives a hint at its origin: pigment in the lower nail plate stems from the distal matrix, that in the medial layers from the medial matrix, and that in the dorsal nail plate from the proximal matrix. Pigment in the entire thickness of the nail means that the whole length of the matrix is involved. The colour may reach from light brown to black, but in Caucasians different shades of brown are the commonest. The band forms when a focus of pigment-producing melanocytes consistently gives more melanin to the onychocytes than they can degrade normally so that they still contain pigment granules during the process of onychisation. However, the demonstration of melanin in the nail alone does not allow a diagnosis to be made. A biopsy from the origin of the stripe, the matrix is necessary; a nail bed biopsy is too distal and will not give the information required.
pigmentation in dark-skinned persons
Melanin-induced brown to black streaks in the nail are rare in fair-skinned persons, but rather the rule in dark-skinned people. Since dark-skinned individuals develop melanomas much less frequently than light-skinned ones, however, acral lentiginous and ungual melanomas are as frequent as in fair-skinned, the differential diagnosis may be very difficult. Brown pigmentation of many finger and toenails are in favour of a benign process. When a single streak stands out by a jet-black coloration a malignant melanoma should be suspected and a histopathological examination of a matrix biopsy is mandatory.
There are no clinical criteria to reliably differentiate a benign or malignant melanonychia. Some observations are in favour of a malignant process:
- The pigmentation developed at age >30 years
- The acquired stripe is wider than 5mm
- The streak develops a periungual pigmentation: Hutchinson's melanotic whitlow
- The pigment stripe darkens or becomes wider proximally indicating growth of the pigment cell nidus in the matrix
- A nail dystrophy develops in the pigmented area
- An erosive or bleeding nodule develops.
Melanonychia striata longitudinalis usually reflects a circumscribed increase in the number of melanocytes, a Lentigo or a junctional melanocytic naevus; however, even at that age subungual melanoma may occur[36-38]. We therefore advocate a histological examination to rule out malignant melanoma. Since most dermatologists are not experienced in taking a nail matrix biopsy, this is often performed too late.
There are different possibilities to take a biopsy for the diagnosis of a longitudinal melanonychia[28-30].
1. Pigment band in the lateral third of the nail: lateral longitudinal nail biopsy
Starting at the distal dorsal crease of the distal interphalangeal joint, a straight incision is carried out down to bone through the proximal nail fold, matrix, nail bed, nail plate and hyponychium medial from the stripe in the nail plate. A second incision is performed parallel to the first one but along the lateral nail plate margin and in the lateral nail groove. This slender long tissue block is dissected from the bone using pointed curved iris scissors. Care has to be taken not to leave remnants of the lateral matrix horn, behind from which a recurrence might develop. The defect is closed with back-stitches that elevate the lateral nail fold, thus improving the cosmetic aspect after the biopsy[39, 40]. This biopsy leaves a narrower, but otherwise normal appearing nail. The tissue block gives an excellent histological overview of the entire pathological process. However, experience from the side of the pathology laboratory is required both in handling of the specimen and of the histopathological interpretation.
2. Localisation of a pigmented
band less than 3mm wide in the median part of the nail: punch biopsy of the
Since a matrix defect of maximally 3mm diameter will only leave a narrow red band after wound healing, a punch of 3mm may be used for very narrow melanonychia. The beginning of the stripe, which is usually hidden under the proximal nail fold, is crucial to biopsy. The punch is run down to bone and the tissue cylinder sectioned at its base with curved pointed scissors. Since the melanocyte focus in the matrix is often larger than anticipated, clinically marginal recurrences are not uncommon. We therefore recommend to remove the nail plate portion overlying the melanocyte nidus and to completely excise it[28,29].
3. Localisation of a pigmented
band less than 3mm wide in the median part of the nail: fusiform excision
A pigmented band in the central portion of the nail that is wider than 3mm does no longer permit a punch excision. The proximal nail wall is incised at both sides and reflected. The overlying nail plate is detached and also reflected to one side. The beginning of the stripe is now visible. This allows the entire melanocytic lesion to be observed and excised in a transverse fusiform manner with a small safety margin of about 1mm. The matrix is gently mobilised and sutured with 6-0 absorbable stitches; care has to be taken not to tie the sutures too tight, in order to avoid their cutting through the fragile matrix tissue. The degree of postoperative nail dystrophy depends on the necessary extent of the matrix excision.
4. Localisation of a wide
pigmented band in the median or lateral nail portion: horizontal excision of
the pigment cell lesion
Our own data and recent publications have shown that longitudinal melanonychia in young persons is most commonly due to a lentigo or junctional naevus in the matrix[37,38,41] (figure 7). Melanocytes are then not found in the dermis. We have therefore developed a biopsy technique that does not leave a cicatricial nail dystrophy. The proximal nail fold is reflected. The proximal third of the nail plate is sectioned transversely, detached from the matrix and opened, allowing the pigment cell focus to be visualised. A very superficial incision is carried around the lesion with a small safety margin. The lesion is horizontally excised in a manner as if taking a free matrix graft. The nail plate, to which the superficial third of the matrix epithelium adheres, is laid back and fixed with two mattress sutures. The proximal nail fold is sutured back. Wound healing was uneventful and without any postoperative nail dystrophy in more than 30 cases operated with this technique[42,43]. The thin slice of tissue is spread out on a little piece of filter paper and then immersed into the fixative. Histological examination is possible without delay. In case of a benign lesion, no further treatment is necessary. In case of a malignant melanoma, a generous re-excision will follow.
Considering the anatomy and histology of nail tumours and respecting the rules of atraumatic sterile surgery, excellent functional and cosmetic results can usually be achieved if the patient comes early enough to surgery10.
Prof. Dr Eckart Haneke
79110 Freiburg im Breisgau
Τel.: 0049 178 5927764
Mob.: 0049 761 8978368
1. Haneke E. Intraoperative differential diagnosis of onychomatricoma, Koenen's tumours, and hyperplastic Bowen's disease. 7th Cong Eur Acad Dermatol Venereol - Eur Nail Soc, Nice. J Eur Acad Dermatol Venereol 1998; 13:Suppl (S119).
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