Reticular erythematous mucinosis (REM) is an uncommon condition in which there is gradual dermal mucin deposition that usually occurs on the mid-chest and back. It occasionally spreads to involve the upper abdomen, neck, and breasts. While the condition favors women in the third and fourth decades of life, it has been reported in men and children. There is no predominant ethnicity or race affected.

Lesions manifest as midline confluent erythematous papules and plaques forming a reticular (net-like) configuration. REM appears to be a disorder of photosensitivity, as a preceding history of intense sun exposure is often elicited. Ultraviolet A (UVA) and ultraviolet B (UVB) both appear to provoke lesions, and further sun exposure usually worsens the condition. In addition, heat, perspiration, and radiation may exacerbate REM. Hormonal influences also seem to play an etiologic role, as oral contraceptives, menses, and pregnancy have been reported to trigger and exacerbate it.

While REM is thought to be limited to the skin, approximately 20% of cases may have systemic comorbidities, such as thrombocytopenia, diabetes mellitus, malignancies, and thyroid disease. Lupus serology is positive only in a small percentage of patients.

Plaque-like cutaneous mucinosis is considered synonymous with REM or is considered to belong to a spectrum of midline mucinosis. Clinically, it is more likely to present as erythematous infiltrated papules and plaques occurring over the midline of the back and chest.