Focal Regression‐Like Changes in Dysplastic Back Nevi :A Diagnostic Pitfall for Malignant Melanoma

Abstract

Regression in melanoma can be complete or partial. Melanocytic nevi may show focal regression‐like changes (RLC). We studied the incidence of RLC in a total of 777 melanocytic back nevi. These included 17 cases of blue nevi, 28 cases of compound nevi, 385 cases of compound dysplastic nevi, 34 cases of congenital compound nevi, 26 cases of congenital intradermal nevi, 58 cases of intradermal nevi, and 229 cases of junctional dysplastic nevi. The dysplastic nevi were categorised according to the associated cytologic atypia (mild, moderate, and severe). 21 malignant melanomas of the back were also reviewed for regression. RLC were seen with a striking correlation with the degree of cytologic atypia in dysplastic nevi. RLC were seen in 4.5% of mildly, 9.6% of moderately, and 17.2% of severely dysplastic compound nevi. RLC were seen in 10.3% of mildly, 18.8% of moderately, and 39.3% of severely dysplastic junctional nevi. The incidence of regression in non‐dysplastic nevi was much less, ranging from 2.9% to 3.6%. We believe this phenomenon is probably related to trauma/irritation. Caution should be taken before rendering the diagnosis of regressed malignant melanoma on the back since dysplastic nevi may show focal similar changes.