Generalised Pruritus

Definition

•    Persistent itching without obvious rash

•    Can severely impact sleep and quality of life

Systemic causes to consider

•    Chronic kidney disease (CKD)

o    "Uraemic pruritus," especially in dialysis patients

•    Cholestasis (liver disease)

o    Worse on palms and soles, may precede jaundice (e.g., PBC, PSC, intrahepatic cholestasis of pregnancy)

•    Haematological disorders

o    Hodgkin lymphoma (classically worse after hot baths/alcohol)

o    Polycythaemia vera (aquagenic pruritus)

•    Iron deficiency anaemia

•    Thyroid disorders

o    Both hyper- and hypothyroidism

•    Diabetes mellitus

o    Especially in poorly controlled patients

Other considerations

•    Drug-induced (e.g., opioids, hydroxychloroquine)

•    Paraneoplastic syndromes

Urticaria

Clinical features

•    Transient wheals (hives): raised, erythematous, often with pale centre

•    Angioedema: deeper swelling affecting lips, eyelids, tongue, larynx; may be life-threatening

•    Individual lesions usually resolve within <24 hours without scarring

Triggers

•    Allergens: foods (nuts, shellfish), drugs (penicillins, NSAIDs)

•    Physical triggers:

o    Cold (cold urticaria)

o    Pressure (delayed-pressure urticaria)

o    Heat or exercise (cholinergic urticaria)

o    Sunlight (solar urticaria)

•    Infections: viral URTIs (common in children)

Chronic urticaria

•    Defined as persisting >6 weeks

•    Often idiopathic

•    Can be autoimmune (autoantibodies to FcεRI on mast cells)

Treatment

•    First-line: non-sedating antihistamines (e.g., cetirizine, loratadine)

•    Increase dose up to fourfold if needed

•    Corticosteroids: short course for severe flares

•    Omalizumab: for severe chronic cases unresponsive to antihistamines

Mastocytosis

Cutaneous form: urticaria pigmentosa

•    Brownish macules or papules → urticate on stroking (Darier’s sign)

•    Due to local mast cell degranulation

Systemic mastocytosis

•    Flushing, pruritus, anaphylaxis, GI symptoms

•    Increased serum tryptase

Diagnosis

•    Skin biopsy: dense mast cell infiltrates

•    KIT mutation (c-KIT)

Treatment

•    Avoid triggers (e.g., NSAIDs, opioids, alcohol)

•    Antihistamines, mast cell stabilisers (e.g., ketotifen)

•    Epinephrine autoinjector if risk of anaphylaxis

Extra Revision Pearls

•    Aquagenic pruritus: consider polycythaemia vera (JAK2 mutation)

•    Darier’s sign: highly suggestive of mastocytosis

•    Urticaria + systemic symptoms (e.g., hypotension, wheeze): think anaphylaxis → IM adrenaline

•    Chronic urticaria rarely associated with systemic disease (unlike pruritus)