This 51-year-old has a long history of hyperthyroidism and fairly recently developed ill-defined plaques on the extensor surfaces of her lower extremities. The biopsy was submitted to rule out panniculitis. This is a classic case of pretibial myxedema. Patients often have a history of hyperthyroidism, although the skin manifestations may not correlate with the level of hyperthyroidism. The etiology is uncertain, but fibroblastic stimulators/growth factors have been implicated. The histology shows copious amounts of mucin within the interstitium, sometimes in the deep dermis and other times in the superficial reticular dermis, as in this case. Mucin stains confirm the diagnosis.
Histologic sections of skin show epidermal papillomatosis and acanthosis with a band-like deposition within the superficial reticular dermis. The extracellular space is expanded, splaying collagen fibers and leaving only a sparse cellular network of spindled-to-stellate cells. The matrix deposits around vascular and adnexal structures, without distortion.