Scleromyxedema without monoclonal gammopathy: Diagnostic and therapeutic implications in the setting of subclinical hypothyroidism

Scleromyxedema (SM) is a rare fibromucinous disorder typically associated with monoclonal gammopathy, but atypical variants without paraproteinemia and with coexistent thyroid dysfunction challenge traditional diagnostic criteria. An elderly male presented with progressive pruritic skin thickening and waxy papules on the limbs and trunk, exhibiting classic SM signs including the “Shar-Pei sign” and “doughnut sign.” Laboratory evaluation revealed subclinical hypothyroidism (elevated thyroid-stimulating hormone and anti-thyroid peroxidase antibodies) but no paraproteinemia or other systemic abnormalities. Histopathology confirmed dermal mucin deposition, fibroblast proliferation, and fibrosis, supporting a diagnosis of atypical SM. The patient was treated conservatively with narrowband ultraviolet B (NB-UVB) phototherapy and levothyroxine (initially 25 µg/day, increased to 50 µg/day). Within 4 months, marked improvement was observed, including resolution of pruritus, flattening of papules, reduced induration, and restored mobility, sustained at 1-year follow-up. This case highlights that thyroid dysfunction should not preclude SM diagnosis, advocating for clinicopathologic correlation and longitudinal monitoring. Conservative therapies such as thyroid hormone replacement and NBUVB phototherapy may provide effective, accessible alternatives in select atypical cases, potentially expanding management options for this challenging condition.