Serum sickness-like reaction to a second generation antipsychotic drug

Introduction: Serum sickness is a type III hypersensitivity reaction. Immune complex deposition activates complement pathways resulting in fever, vasculitic rash, arthritis and lymphadenopathy. Medications are known to trigger serum sickness-like reactions which clinically resemble serum sickness, however, are not thought to involve circulating immune complexes. The full pathophysiology is not clear. Risperidone is an atypical antipsychotic drug commonly used in the paediatric population.

Aim: To describe the diagnosis, disease course and outcome of a patient who developed serum sickness-like reaction secondary to risperidone.

Methods: Review of patient chart and medical interview in accordance with institutional research ethics board approval.

Results: The patient, a 7 year old male with Attention Deficit Hyperactivity Disorder, was started on risperidone 0.25 mg once daily. Within a week the dose was increased to 0.5 mg once daily. During the third week after initiation of medication, the patient developed generalized purpuric, confluent, maculopapular rash. Although the patient did not have any signs and symptoms of a viral illness, he was diagnosed with viral-induced exanthema and continued on risperidone. On day 28, he developed significant, bilateral swelling of upper and lower extremities, facial angioedema, lymphadenopathy, arthralgia and arthritis in ankles, knees, hands and elbows without fever. Investigations showed normal complement C3 and C4 levels. C1 esterase inhibitor, anti-nuclear antibody and urinalysis were normal. Erythrocyte sedimentation rate, C-reactive protein and leukocyte levels were elevated. The diagnosis of serum sickness-like reaction to risperidone was made and the patient subsequently treated with cetirizine, hydrocortisone, and prednisone for 1 week with significant improvement. Skin biopsy was declined by the patients’ parents and therefore was not performed. Provocative oral challenge to risperidone was not considered because of clear suggestive history and ethical consideration.

Conclusion: Psychotropic medications are known to cause cutaneous eruptions. Serum sickness-like reactions can happen upon exposure to risperidone. Clinicians should be aware of this potential adverse reaction that can develop weeks after therapy initiation, and be encouraged to discontinue risperidone when the suggestive symptoms emerges.

Statement of novelty: We describe a case of serum sickness-like reaction to risperidone in a paediatric patient. To our knowledge, this is the first case of serum sickness-like reaction to risperidone.