Allergy to benzalkonium chloride in plaster of Paris after sensitisation to cetrimide. A case report.

A five-year-old boy presented with a simple undisplaced fracture of the lower end of the left radius. An above-elbow plasterwas applied and he was sent home. Twenty-four hours later a “ plaster check” revealed a swollen hand and the patient complained of intense pain. There was a rash on the left anterior abdominal wall and he was mildly febrile (38.3 degrees Celsius). The plaster was removed and marked erythema and oedema were noted on the lower arm, forearm and hand. A forearm plaster back-slab was applied and the opinion of a paediatrician was sought to exclude a coincidental viral illness. A few hours later the boy returned with a more swollen hand and blistering of the skin in the erythematous area (Fig. 1). He was admitted to hospital, the limb was elevated, the blisters were cleaned and dressed and two ‘weeks later both bone and skin were completely healed. The abnormalities in the skin were restricted to those parts of the left arm whiclf had been covered by the plaster of Paris. The lesions on his left anterior abdominal wall were compatible with contact of the cast with the skin during the night after the injury and treatment. The possibility of a contact dermatitis was investigated as follows.