A 41-year-old white man is described with papules of the lower and upper back, the neck and the upper chest, a marked deposition of mucin in the upper reticular dermis, and an IgG lambda monoclonal gammopathy strongly evocative of scleromyxedema (lichen myxedematosus). Additionally, he developed intense myalgia, muscle weakness and rhabdomyolysis, which were associated with heliotrope erythema, photosensitivity and an erythematous rash of the dorsum of the hands with Gottron's papules. Muscle biopsy revealed an inflammatory myositis, and dermatomyositis was diagnosed. The association of dermatomyositis and secondary mucinosis, or muscle involvement in primary papular mucinosis are not rare. However, the association between scleromyxedema and dermatomyositis has only exceptionally been reported.