Reticular erythematous mucinosis

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Reticular erythematous mucinosis (REM) is a skin condition caused by skin cells called fibroblasts making too much mucin, a jelly-like substance. It mostly affects women in their 30s and 40s. People develop small bumps and pink to red patches that blend into net‑like, ringed patterns. These patches usually appear on the upper back or chest, but they may also show up on the face, arms, legs, or abdomen. The skin changes can itch a little and may include visible tiny blood vessels (telangiectasias). Sun exposure often worsens REM, though in rare cases sunlight can help. Light-based skin tests can trigger REM lesions in some people.

REM can occur with other conditions, such as thyroid disease (including Hashimoto’s), myxedema, monoclonal gammopathy, and HIV infection. Triggers that can start or worsen REM include menstruation, heat, X-ray therapy, hormonal birth control, pregnancy, and sweating. There is ongoing research about a possible link to lung cancer.

What happens in REM at the tissue level: there is variable inflammation around blood vessels in the skin and excess mucin in the upper and middle layers of the skin. Staining tests for mucin can vary. Some patients also show immune deposits, such as IgM, at the dermal-epidermal junction. Under electron microscopy, there may be changes in skin cells and fibroblasts.

Treatment: Antimalarial drugs, especially hydroxychloroquine 200–400 mg per day, are the preferred therapy and often produce a quick improvement, though the condition may recur after stopping treatment. Other treatments tried with variable success include oral antihistamines, topical tacrolimus, corticosteroids (oral or topical), tetracycline antibiotics, cyclosporine, and UVB light therapy.