🩺 Generalised Rash

Generalised rash refers to an extensive eruption affecting multiple body regions, often presenting as a diagnostic challenge due to the overlap between infectious, inflammatory, and allergic causes. In the UK, it ranges from common viral exanthems in children to life-threatening dermatological emergencies in adults. The primary goal of clinical assessment is to exclude systemic instability and identify high-risk triggers, such as new medications or underlying systemic disease. Treatment is directed at the underlying cause, supported by emollients and antihistamines for symptom relief.

Inquire about the speed of onset, associated pruritus or pain, and systemic symptoms like fever or malaise. Conduct a thorough medication history (including antibiotics and anticonvulsants) and ask about recent travel, unwell contacts, or new topical products. Assess for 'red flag' symptoms such as shortness of breath or tongue swelling (anaphylaxis) and blistering or skin tenderness (toxic epidermal necrolysis).

Assess for systemic stability (ABCD) and the percentage of Body Surface Area (BSA) involved. Describe the morphology (maculopapular, vesicular, pustular, or urticarial) and distribution (symmetrical, dermatomal, or flexural). Check for mucosal involvement (eyes, mouth, genitals) and Nikolsky’s sign (epidermal peeling with lateral pressure). Palpate for lymphadenopathy and assess for hepatosplenomegaly, which may indicate systemic drug reactions or haematological malignancy.

Viral exanthem (e.g., Measles, Rubella, Parvovirus B19), Drug eruptions (Morbilliform, DRESS, SJS/TEN), Urticaria, Eczema/Dermatitis, Psoriasis, Pityriasis rosea, Scabies, and Secondary Syphilis.

Skin tenderness/pain, mucosal involvement (mouth/eyes/genitals), blistering/skin peeling (Nikolsky's positive), high fever with systemic malaise, and any signs of airway compromise or hypotension.

Initial tests depend on clinical suspicion but often include FBC (eosinophilia in DRESS), U&Es, LFTs, and CRP. Skin swabs are indicated if secondary infection is suspected, while skin biopsies (incisional or punch) are definitive for complex inflammatory or neoplastic causes. Immunofluorescence may be required for bullous disorders. If vasculitis is suspected, perform a urine dip and consider ANCA/ANA/Complement levels.

Always differentiate between 'dermatology emergencies' (SJS/TEN, Erythroderma, DRESS) and benign viral exanthems. A 'drug history' must include all over-the-counter supplements and changes in the last 8 weeks. Palpable purpura always warrants a vasculitis workup, including a urine dipstick for haematuria/proteinuria. In dark skin tones, erythema may appear violaceous or hyperpigmented rather than bright red.

Mapped to 'Acute Rash' and 'Chronic Skin Conditions' in the MLA content map. Students must recognise the life-threatening nature of SJS/TEN and the importance of urgent dermatological referral for erythroderma (>90% BSA). Understand the role of topical steroids versus emollients.