6472 Methimazole Induced Agranulocytosis: Uncommon Complication of a Common Medication

Abstract Disclosure: R. Kaur: None. L. Kaur: None. A. Sridhar: None. T. Chaudhary: None. N. Patel: None. Methimazole (MMI) induced agranulocytosis is a rare and life threatening adverse effect that usually occurs within 3 months of drug initiation and can rapidly lead to overwhelming infection. It is reported in 0.1 to 0.5 % of patients on treatment with methimazole. MMI is a standard drug used in graves disease and toxic multinodular goiter. We report a case of MMI induced agranulocytosis in an elderly female with recently diagnosed toxic multinodular goiter. A 66 year old female with past medical history of recently diagnosed toxic multinodular goiter for which she was started on methimazole 80mg/day two months ago presented to the emergency department with chief complaint of severe sore throat associated with rapidly increasing pharyngeal pain and fever over the past 24 hours. She was lethargic, febrile with temperature of 102 F, tachycardic with heart rate of 115/minute and hypotensive with blood pressure of 108/64 mm Hg. Physical examination revealed diffuse pharyngeal and tonsillar erythema with bilateral purulent exudate with tender anterior cervical lymphadenopathy. Thyroid was enlarged, firm, irregular and nontender. Pulmonary, cardiac and abdominal exam was unremarkable. Lab work showed severe leukopenia with WBC count of 1,600/mm3, neutropenia with absolute neutrophil count of 0.0 x 1000/ul (normal range 1.8-7.3 x 1000/ul) and erythrocyte sedimentation rate and C reactive protein were both elevated. Blood cultures and fungal cultures showed no growth. Urinalysis and urine culture were both unremarkable. She had an extensive haematological, rheumatological and infectious disease workup for neutropenia, which was largely unrevealing. Rapid streptococcal testing was negative but throat cultures grew beta haemolytic streptococci. Treatment included suspending methimazole, administering antimicrobial therapy with piperacillin - tazobactam, acyclovir and fluconazole. She was also started on a granulocyte colony stimulating factor. Patient presented satisfactory evolution with progressive increase in leukocyte count and remission of symptoms by day 5 of treatment, rendering further bone marrow testing unnecessary. Antibiotics were changed to oral amoxicillin-clavulanic acid after throat culture results were available and the patient was discharged in stable condition. One month after discharge she underwent total thyroidectomy for definitive cure and is currently followed up as an outpatient by endocrinology. The objective of this case report is to present an uncommon case of agranulocytosis secondary to use of methimazole and to increase awareness among the physicians about the need to consider this diagnosis in patients on this medication. It is also advised that these patients be educated about the drugs side effects, a practice that may avert suffering and unnecessary costs. Presentation: 6/3/2024