#dermpathjc January 2019:

 

Journal Club summary:

This month’s journal club article discussed a topic that gives many of us much consternation, pigmented lesions of the nail unit. The article was a good overall review in many regards; there was discussion (with images) of the clinical features of melanocytic lesions and the concerning signs, as well as a review of the epidemiology, histology, and molecular findings. The learning objectives for the article were very well laid out, and there are accompanying CME questions for obtaining AMA PRA Category 1 credits.

It was a lively discussion, and those active in the discussion overall agreed with the author’s summary and findings.

There were a few take home points from the paper and subsequent discussion, which touched on all aspects:

Embryology:

• Proximal nail matrix = predominantly dormant melanocytes
• Distal nail matrix = active and dormant melanocytes (more likely for a melanocytic lesion to arise within this zone)

Epidemiology:

• Melanocytic macule more common in adults
• Nevi more common in children

Clinical:

• Longitudinal melanonychia not always due to a melanocytic lesion (Fungus, drugs, trauma, infection, etc can be causative)
• Amelanotic subungual melanoma has been reported at rates between 15-50% (while they only comprise 2-8% of melanomas at other sites)

Sampling:

• Many seem to groan with nail clippings to evaluate for a melanocytic lesion
• If clippings are sent, if negative they will usually be emblazoned with a caveat in an comment

Histology:

• Most peoples malignant lesions have been composed of melanoma in situ with invasive melanoma making up the minority.

Immunohistochemistry:

• SOX10 not as useful in the nail unit as in other parts of the body
• Mart-1 / Melan A are preferred, and felt to work better
• Some also order a Fontana Mason in addition

Molecular:

• Subungual melanoma more commonly harbor KIT mutations
• Predictions through immunohistochemistry has thus failed to be predictive of molecular aberrations
• Gold standard for interrogation of KIT mutations remains molecular analysis

Some Highlights from the Evening:

Top: nail plate chromomycosis

Bottom: nail plate onychomycosis

The conversations were great again, with a nice mix of Dermatologists and Pathologists from all over the world. Hope to see you again next time!