DP20: Reticular erythematous mucinosis: a rare case of primary dermal mucinosis

T. Nasreen, H. Sazali and C. Feighery

Our Lady of Lourdes Hospital, Drogheda, Ireland

Reticular erythematous mucinosis (REM) is a rare, idiopathic disorder of primary dermal mucin accumulation, characterized by maculopapular reticular erythema or plaques commonly on midline, upper back and chest (Cinotti E, Merlo V, Kempf W et al. Mucinosis: histopathological and immunohistochemical features of 25 patients compared with 25 cases of lupus erythematosus tumidus. J Eur Acad Dermatol Venereol 2015; 29: 689–97). Histology demonstrates superficial and deep perivascular and periadnexal lymphocytic infiltration with abundant mucin. Other conditions bearing resemblance to REM include lupus erythematosus tumidus (LET), dermatomyositis and scleroderma. Early and correct diagnosis is important to exclude the abovementioned diseases as REM is more benign and has fewer systemic consequences. Common features shared by REM and LET are erythematous plaque-like clinical aspect of lesions. However, photosensitivity – rare in REM – is almost always present in LET. Histologically, REM tends to show more scattered superficial lymphocytes with abundant superficial and deep mucin, less frequent immunoglobulin and reduced complement depositions along the dermoepidermal junction than LET. This suggests the distinction of the two diseases and different pathogenetic mechanisms. We report the case of 26-year-old woman whose REM was found to be correlated with smoking, sun exposure and a hot environment. She had an ongoing pruritic rash on her chest and back for 3 years, with intermittent breast tenderness causing her difficulty in wearing a bra. Her family history was not contributory. Examination demonstrated symmetrical reticular macular erythema on her central back and chest, with some discrete erythematous papules on the medial aspect of the breasts. She remained nonrespondent to topical miconazole, hydrocortisone, fusidic acid and betamethasone valerate. Investigations, including full blood count, serum biochemistry, antinuclear antibody, extranuclear antibodies, and C3 and C4 levels, were normal. Patch test was positive for nickel and fragrance mix. Initial differentials were allergic dermatitis/tumid lupus/REM/scleroderma. Punch biopsy revealed normal epidermis with superficial and deep perivascular and perifollicular lymphocytic inflammatory infiltrate, with a copious amount of mucin between collagen fibres of the dermis. Mucin stain was positive. A clinicopathological diagnosis of REM was made. Allergic dermatitis was a red herring. She was started on hydroxychloroquine and showed remarkable improvement over a few weeks. This case expands our current knowledge of the clinical presentation of this rare midline dermal disorder of mucinosis, which is often recalcitrant to multiple treatment modalities. Antimalarial treatment is considered the most effective approach. To our knowledge, only a few cases exist on its use in REM.