mucinosis

Mucinosis, or mucinoses, comprises disorders characterized by abnormal accumulation of mucin in the skin or other tissues. Mucin refers to gel-like glycosaminoglycans, mainly hyaluronic acid, produced by dermal fibroblasts. Excess mucin can produce edema, papules, plaques, or thickened skin, depending on the pattern and distribution.

Most mucinoses are cutaneous and fall into primary forms, where mucin deposition occurs in the skin without an identifiable systemic disease, or secondary forms, where mucin accompanies another condition such as thyroid disease, lupus, scleroderma, or inflammatory or neoplastic processes. Major cutaneous subtypes include lichen myxedematosus (papular mucinosis) and scleromyxedema, as well as pretibial myxedema and other localized variants.

Lichen myxedematosus presents as localized waxy papules, commonly on the trunk and proximal limbs. Scleromyxedema is a generalized papular and sclerodermoid eruption often with dermal mucin and fibroblast proliferation, and it may be associated with a monoclonal gammopathy and systemic involvement affecting the GI tract, lungs, or nervous system.

Diagnosis relies on skin biopsy showing dermal mucin between collagen fibers; Alcian blue staining is typically positive. Laboratory workup screens for underlying or associated conditions, including thyroid function tests and monoclonal gammopathy testing when scleromyxedema is suspected.

Treatment is tailored to subtype and severity. Localized mucinoses may respond to topical therapies or phototherapy, while scleromyxedema often requires systemic treatment such as intravenous immunoglobulin, retinoids, immunosuppressants, or plasmapheresis. Prognosis varies by subtype and systemic involvement, with scleromyxedema carrying potential for progressive disease and complications.