Fever, urticaria, lymphadenopathy, and protracted arthralgia and myalgia resistant to corticosteroid therapy.

Allergen immunotherapy is commonly incorporated in the management of allergic rhinoconjunctivitis, allergic asthma, and insect sting hypersensitivity. It is generally safe, but systemic reactions occasionally occur, mainly of the immediate type and rarely of the delayed type. We report a case of a 50-year-old man with allergic rhinoconjunctivitis on immunotherapy for 3 years and then received an injection from another patient's extract. The latter contained a higher concentration of house-dust mite and pollens of grasses, trees, and weeds. It also contained molds that the patient's correct extract did not have. Within half an hour, he developed a systemic reaction that resolved with symptomatic treatment. Two weeks later, he received one-half of his usual immunotherapy dose. Within a week, he developed urticaria, arthralgia, myalgia, fever, and lymphadenopathy. Laboratory abnormalities included leukocytosis, elevated erythrocyte sedimentation rate, hematuria, and elevated liver enzymes. Oral corticosteroid therapy for 3 weeks was ineffective. He developed significant myalgia and apparent mood changes, attributable to corticosteroid intake. After a single plasmapheresis, he felt remarkable improvement within <24 hours. Corticosteroid therapy was gradually withdrawn over 10 weeks without relapse of symptoms. This is a rare case of probable serum sickness after the administration of a wrong allergy immunotherapy extract. However, a causal relationship could not be proven. The response was poor to prolonged corticosteroid therapy but was remarkable to one plasmapheresis.