Late-onset amyloidosis cutis dyschromica: A rare case of progressive dyschromia caused by compound heterozygous GPNMB mutation

Amyloidosis cutis dyschromica (ACD) is a rare form of primary cutaneous amyloidosis characterized by hypopigmented and hyperpigmented macules and patches without systemic involvement. Typically benign, ACD involves amyloid deposition in the papillary dermis. Mutations in the glycoprotein nonmetastatic gene B (GPNMB) gene, which is implicated in melanosome formation, as well as ultraviolet hypersensitivity and DNA repair defects, contribute to dyschromia. A 34-year-old female presented with a 10-year history of asymptomatic, mottled pigmentary macules and patches on the upper and lower extremities. A skin biopsy showed widened dermal papillae containing eosinophilic amorphous deposits, highlighted in Congo red stain and cytokeratin 5/6 immunostaining, which confirmed the diagnosis. Furthermore, whole-exome sequencing identified a nonsense (Arg189Ter) and a missense variant (Cys425Ser) in GPNMB . It is essential for understanding the hereditary component and guiding counseling. Management primarily addresses cosmetic concerns. For this patient, strict photoprotection and oral antioxidants, such as vitamins C and E, were recommended.