Discoid rash

Discoid rash represents the most common form of chronic cutaneous lupus erythematosus. Lesions typically appear on sun-exposed areas such as the face, scalp, and ears, presenting as erythematous, indurated plaques with adherent scale, follicular plugging, and central atrophy. Over time, lesions heal with scarring, dyspigmentation (hypo- or hyperpigmentation), and can cause scarring alopecia if they involve the scalp. Histopathology shows interface dermatitis with vacuolar degeneration of the basal layer, follicular plugging, and a perivascular/periadnexal lymphocytic infiltrate; direct immunofluorescence may show granular IgG/IgM and complement deposition at the dermoepidermal junction (positive "lupus band test"). While most patients with discoid lupus have skin-limited disease, approximately 5-10% may progress to systemic lupus erythematosus, and discoid rash is one of the 11 classic diagnostic criteria for SLE (now incorporated into the SLICC/ACR and EULAR/ACR classification systems). Clinically, it's important to distinguish discoid rash from the malar (butterfly) rash of acute cutaneous lupus, which is non-scarring and spares the nasolabial folds. Management includes sun protection, topical or intralesional corticosteroids, topical calcineurin inhibitors, and antimalarials (e.g., hydroxychloroquine) for more extensive disease. Smoking cessation is also recommended as smoking can reduce the efficacy of antimalarial therapy.