Write a short note on the mucocutaneous manifestations of systemic lupus erythematosus.

Introduction

Skin and mucous membrane involvement occurs in over 80% of patients with SLE and is frequently the presenting feature. Four of the classification criteria for SLE are mucocutaneous — acute cutaneous lupus, chronic cutaneous lupus, oral ulcers and non-scarring alopecia — so recognising these lesions is central to diagnosis.

Classification of Lupus-specific Skin Disease

1. Acute cutaneous lupus erythematosus

• Malar ("butterfly") rash — erythema over the cheeks and bridge of the nose, characteristically sparing the nasolabial folds. Photosensitive, transient, heals without scarring. Distinguish from rosacea (which has papules, pustules and telangiectasia) and from dermatomyositis (which involves the nasolabial folds and eyelids).
• Generalised maculopapular eruption on sun-exposed areas, often coinciding with disease flare.
• Correlates with active systemic disease and raised anti-dsDNA.

2. Subacute cutaneous lupus erythematosus (SCLE)

• Annular polycyclic or papulosquamous (psoriasiform) lesions on the upper trunk, shoulders and extensor arms; markedly photosensitive; heals with dyspigmentation but no scarring.
• Strongly associated with anti-Ro (SSA) antibodies.
• Drug-induced SCLE — hydrochlorothiazide, terbinafine, calcium channel blockers, proton pump inhibitors, anti-TNF agents.
• Mothers with anti-Ro are at risk of neonatal lupus and congenital heart block in the infant.

3. Chronic cutaneous lupus — discoid lupus erythematosus (DLE)

• Well-defined erythematous plaques with adherent scale, follicular plugging ("carpet-tack" sign on removing scale), healing with central atrophy, scarring and dyspigmentation — hypopigmented centre with hyperpigmented rim, particularly conspicuous in Indian skin.
• Sites: face, scalp, ears (especially conchal bowl) and neck.
• Scarring alopecia where the scalp is involved — permanent, and a strong reason for early treatment.
• Only about 5–10% of patients with isolated DLE progress to systemic lupus, but 20–25% of SLE patients develop DLE lesions.

Non-specific Mucocutaneous Features

• Photosensitivity — an exaggerated rash after sun exposure, present in the majority.
• Oral and nasal ulcers — classically painless, on the hard palate and nasal septum; painless ulceration distinguishes them from aphthous ulcers.
• Alopecia — diffuse non-scarring hair loss with fragile "lupus hairs" at the frontal hairline during flares (reversible), contrasted with the scarring alopecia of discoid lesions (permanent).
• Vasculitis — palpable purpura, periungual erythema, nailfold infarcts, splinter haemorrhages, digital ulceration.
• Raynaud's phenomenon — triphasic colour change of digits on cold exposure.
• Livedo reticularis — a net-like violaceous mottling, strongly associated with antiphospholipid antibody syndrome.
• Bullous lupus, urticarial vasculitis, chilblain lupus, lupus panniculitis (profundus) and periorbital oedema.

Investigations

• ANA (positive in over 95%), anti-dsDNA (specific, correlating with activity and nephritis), anti-Sm (highly specific), anti-Ro/La, complement C3 and C4 (low in active disease), CBC (cytopenias), urinalysis for proteinuria and casts, and renal function.
• Skin biopsy shows interface dermatitis with basal vacuolar change
• direct immunofluorescence demonstrates the lupus band test — granular IgG, IgM and C3 at the dermo-epidermal junction, positive in lesional skin.

Management

• Photoprotection is fundamental — broad-spectrum sunscreen with high SPF applied daily and reapplied, protective clothing, wide-brimmed hats, avoidance of midday sun. Counsel that ultraviolet exposure can trigger systemic flares, not only skin lesions.
• Stop smoking — smoking worsens cutaneous lupus and reduces the efficacy of antimalarials.
• Topical corticosteroids and topical calcineurin inhibitors for localised disease; intralesional steroid for resistant discoid plaques.
• Hydroxychloroquine — the cornerstone systemic agent for cutaneous lupus; also reduces systemic flares, thrombosis and mortality in SLE. Requires baseline and periodic ophthalmological screening for retinopathy.
• Systemic corticosteroids for severe or widespread disease, with steroid-sparing agents — methotrexate, mycophenolate mofetil, azathioprine — and belimumab or rituximab in refractory systemic disease.
• Review drugs that may induce lupus — hydralazine, procainamide, isoniazid, minocycline, anti-TNF agents.