Specificity of dermal mucin in the diagnosis of lupus erythematosus: comparison with other dermatitides and normal skin.

Increased dermal mucin is a feature of lupus erythematosus (LE); however, its amount and distribution have not been well characterized. The differentiation of LE from other forms of dermatitis can be challenging when other features of LE are subtle or equivocal. One hundred and thirty-five skin specimens showing LE, graft vs. host disease, erythema multiforme/fixed drug eruption, lichen planus, polymorphous light eruption (PMLE), urticaria, eczematous dermatitis and psoriasis and normal skin with and without photodamage were collected. The amounts of mucin in the papillary, superficial reticular and deep reticular dermis were scored from 0 to 3 on hematoxylin-eosin (H&E) and alcian blue (AB) stains, and compared between groups. The mean scores in the reticular dermis were significantly higher in LE than in other categories except PMLE and eczematous dermatitis. A combined H&E + AB score of ≥5 in the superficial reticular dermis gave an overall specificity of 85.7% for LE. Mucin in the papillary dermis failed to distinguish among entities. Normal photodamaged skin showed significantly more mucin in the superficial reticular dermis compared to non-photodamaged skin. While LE is associated with increased mucin deposition, scant to moderate amount of mucin alone has limited specificity and is common in other dermatitides or photodamaged skin.