Spanning 17 Years: Diagnostic Evolution from Lichen Planus Pigmentosus to Hyperpigmented Mycosis Fungoides.

Lichen planus pigmentosus (LPP) and hyperpigmented mycosis fungoides (MF) represent two distinct rare cutaneous disorders. This case explores the potential association between LPP and hyperpigmented MF, a previously unreported progression. The authors report a 52-year-old male presenting with purplish-red macules on the abdomen and upper extremities subsequent to exposure to petrochemicals, initially diagnosed in 2007 with lichen planus (LP). In 2019, LPP was confirmed by histopathological evaluation of a skin biopsy obtained from an outside institution. Despite treatment with hydroxychloroquine sulfate tablets, the lesions exhibited disease progression. After 17 years, generalized hyperpigmentation gradually developed. Repeat biopsies and immunohistochemistry were performed in 2024, leading to the definitive diagnosis of hyperpigmented MF. The patient is currently managed with subcutaneous interferon alpha-2b (IFNα-2b) injections, with the rash color showing slight lightening. In conclusion, the cutaneous manifestations of MF demonstrate marked heterogeneity, requiring systematic clinical evaluation and histopathological assessment to facilitate accurate diagnosis and guide the development of stage-appropriate treatment protocols. Whether the transformation from LPP to hyperpigmented MF is rare, impossible, or a missed diagnosis remains to be further clarified with more reported cases.