This 63-year-old African-American woman presented to dermatology with a 1-year history of an asymptomatic nodule on her right shin. The lesion was biopsied to rule out panniculitis. Following the biopsy findings, a remote history of poorly controlled hyperthyroidism was ascertained. This histology is classic for pretibial myxedema. The etiology is unclear, but it is often seen in patients with hyperthyroidism. The pathogenesis is thought to relate to circulating fibroblastic stimulating factors, causing production of mucinous matrix.
Histologic sections of skin show a band-like area of clear matrix deposition with increased intercellular space at mid-dermal levels. The deposition is ill-defined, not forming a discrete mass. The adnexal structures are undisturbed. The overlying epidermis is slightly acanthotic.