Rationale: Azathioprine is a purine analog (PA) used to treat myasthenia gravis (MG). However, some patients are sensitive to azathioprine and develop severe side effects, such as leukopenia, alopecia, and diarrhea soon after using the medication. Pharmacogenetics plays a crucial role in such intolerance.
Patient concerns: A 16-year-old woman with MG developed hair loss, pancytopenia, bloody diarrhea, and fever shortly after azathioprine treatment.
Diagnosis: Pharmacogenetic analysis revealed compound heterozygosity of the nudix hydrolase 15 (NUDT15) gene, which led to suppressed NUDT15 function. Colonoscopy revealed large ulcers with polypoid lesions in the terminal ileum, cecum, ascending colon, and rectum. These are the characteristics of inflammatory bowel disease (IBD).
Interventions: Sanger sequencing of NUDT15 gene and colonoscopy for bloody stool evaluation.
Outcomes: The patient recovered completely from this acute episode after discontinuation of azathioprine treatment. Her hemogram turned back to normal range. There was also no blood in stool during follow-up.
Lessons: Pharmacogenetic effects should be considered when prescribing PA medication. The possibility of secondary or concomitant autoimmune diseases must always be considered in patients with MG.
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