Onychocytic Matricoma | Dermatopathology

Final Diagnosis: Pigmented Onychocytic Matricoma

Diagnosis comment: The biopsy is most consistent with an onychocytic matricoma based on the hyperplastic bulbous quality of the rete pegs of matrical origin defining the essence of an onychocytic matricoma. It is reasonable to use the adjectival modifier of pigmented to denote the proliferation of lightly pigmented Fontana-Masson, tyrosinase positive dendritic melanocytes within the matrical epithelium.

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Slide 1: The patient is a 75-year-old male who has nail dystrophy. The left thumb was biopsied due to what is perceived as nail dystrophy. The nail biopsy from the left nail includes nail matrix.

Slide 2: The nail matrix epithelium does show variation in thickness.

Slide 3: There is a focal area where the rete pegs are rather bulbous.

Slide 4: At first glance, there is no obvious melanocytic lesion that is apparent. The nail matrix epithelium does not appear particularly pigmented.

Slide 5: The tyrosinase stain highlights the melanocytes within the bulbous hyperplastic area where they are few in number but nevertheless discernible exhibiting a dendritic quality.

Slide 6: Fontana-Masson preparation confirms the minimal melanization pattern that is evident on H&E assessment. A few melanin granules are identified on the superficial corium, and as well, there are dendrites of melanocytic derivation that show a weak staining pattern for Fontana-Masson.