Severe cutaneous adverse drug reaction as a consequence of Allopurinol: The importance of HLA B58:01 testing

A 61-year-old Han Chinese male presented with 4-5 weeks of failure to thrive, hiccups, malaise, and fevers up to 101.5 at home. The patient had been admitted one week prior due to similar symptoms. His primary care physician recently (within 3 months) started gabapentin and chlorpromazine for hiccups, and allopurinol for gout. Drug fever was suspected, and the patient was asked to discontinue gabapentin, allopurinol and chlorpromazine. A short infectious workup for eosinophilia was negative for Herpes Simplex, Strongyloides, and Mycoplasma Pneumoniae, and he was discharged. On repeat admission he admitted to occasional use of allopurinol since his discharge home. Blood pressure was 90/50, temperature was 100.5 Degrees Fahrenheit, and heart rate was 100. Physical exam showed facial plethora, dry mucus membranes, and a diffuse morbiliform rash covering 70 percent of his body. Labs were notable for white blood cell count of 20,000 per microliter, with 6,200 eosinophils per microliter, and 31% eosinophils. Peripheral blood smear confirmed eosinophilia. A skin biopsy showed combined spongiotic and perivascular dermatitis, with eosinophils and neutrophils, all of which was consistent with Severe Cutaneous Adverse Reaction (SCAR). His symptoms quickly improved with oral prednisone. HLA B58:01 allele was positive, which is associated with allopurinol hypersensitivity. The patient was warned to avoid use of allopurinol in the future. HLA B58:01 allele testing in the Han Chinese population is routine in East Asian countries prior to treatment with allopurinol. Despite recommendations by the College of Rheumatology, testing is often overlooked.