60-year-old man complains of black spot on left thumb nail
How long have you had this spot on your nail?
I noticed it at least 5 years ago. I first thought it was a bruise. I'm a mechanic and I am always smashing my thumb. But this spot just won't go away and keep spreading.
A course of months to years is typical for this disorder. Since the lesion is asymptomatic and change slowly, patients often seek case too late.
Does it hurt?
No, it doesn't hurt. It just started to bother me when it broke through the nail about 2 months ago.
The lack of pruritus and pain speaks against an inflammatory disorder. The destruction of adjacent anatomical structures strongly suggests a tumor.
Has it been treated?
Yes; I got some special antifungal nail polish from the drug store, but it didn't help. The spot got bigger.
A nail fungal infection would not grow through the nail and become so nodular. There are forms of fungal infection that cause a dark spot but they are rare. Treating a dark nail spot as a fungal infection without further studies is inappropriate.
Do you work with paints, oils or chemicals which could have discolored the nail?
The oils I used wash off easily. I don't think that's the answer.
This question isn't very useful, as the problem has been present for 5 years. The thumb nail grows out in 4-6 months.
Do you take any medications?
Yes, I take a beta-blocker for high blood pressure and a blood thinner.
It is always important to take a medication history. There are some medications such as zidovudine which discolor the nails. More important in this case, if this lesion is biopsied or excised, the blood thinner will have to be stopped for a few days.
Are you allergic to any medications?
No, I never had problems.
Once again, important when planning treatment. He might be allergic to local anesthetics or antibiotics, which would alter your approach.
Choose the right efflorescences:
The black spot on (or actually below) the nail is a macule. It is irregular, brown-black and > 5 mm. It also involves the cuticle (Hutchison sign).
No fluid-filled lesions are seen here. On the hands, they suggest an acute dermatitis or perhaps a herpetic lesion.
In some areas, the macule has become palpable and thus a papule, such as where it has damaged the nail.
Lichenification is caused by persistent rubbing of the skin and features exaggerated skin markings.
An ulcer is a deep skin defect; this lesion often ulcerates but this has not yet occurred.
Choose the right diagnosis:
A melanocytic nevus can cause nail discoloration. The pigmentation should be symmetrical and stable. The asymmetry, the late onset and beginning destruction of the nail all speak against this diagnosis.
Unfortunately this is an acral lentiginous malignant melanoma which has been overlooked for years. This diagnosis should always be considered in focal nail discoloration, especially in adults. Similar lesions can involve mucosal surfaces. This form of melanoma is the most common variant in Blacks and Asians. There is no relation to sun exposure.
Lentigo simplex can also appear under the nail. It is a small lesion and stable. The asymmetry, the late onset and beginning destruction of the nail all speak against this diagnosis.
Bowen disease can be subungual but it presents as a warty lesion which is therapy-resistant. Thus, all recalcitrant subungual warts in adults should be biopsied to exclude Bowen disease. There is a rare amelanotic (non-pigmented) form of melanoma which can easily be confused with Bowen disease.
Choose the right therapy(ies):
An excisional biopsy is needed to confirm the diagnosis and determine the depth of the melanoma, which will greatly influence therapy. Possibilities include local excision with appropriate margin, sentinel lymph node excision, radical lymph node dissection, further staging procedures)
These agents play no role here.
Radiation therapy is not the first choice for malignant melanoma. In rare cases, when the patient cannot tolerate surgery or when excision with adequate margins is impossible, radiation therapy can be considered.
Chemotherapy may be considered if the patient develops metastatic disease. Prophylactic chemotherapy, immunotherapy or combinations thereof should be part of study protocols.
Phototherapy is not effective against malignant melanoma.