Non‐melanoma Hutchinson's sign: a reappraisal of this important, remarkable melanoma simulant

Abstract Background More than 20 years ago, our reappraisal of the Hutchinson's sign (HS) gave birth to the concept of the pseudo‐Hutchinson's sign. Objectives We have found it interesting to emphasize some important histologic points and to expand the list of the numerous HS simulants. Methods We have examined the cutaneous samples taken from the pigmented skin of patients in association with nail matrix biopsy. We have also extended the long list of non‐melanoma HS based on comprehensive literature review. Results Histologically, HS may present only as an epidermal pigmentation, depending on the area sampled. Occasionally, there may be a sparse junctional melanocytic proliferation which does not demonstrate cytologic atypia due to an underlying melanocytic naevus of the nail matrix. However, early HS often shows a melanoma in situ , with a HS at the proximal nail fold (PNF) and confluent “atypical” melanocytes in the nail matrix. Finally, involvement of the PNF, nail matrix and nail bed containing atypical melanocytes in irregular array may be seen in more advanced lesions. The recent literature on non‐melanoma HS simulants is summarized and clinical examples are provided. Conclusion The mere presence of periungual pigmentation is neither clinically nor histologically pathognomonic of subungual melanoma and justifies the usefulness of this work stressing the non‐melanoma HS.