Thyroid Drug’s Rare Side Effect Triggered Sepsis and a Bowel Emergency in a 36-Year-Old Woman

A routine prescription for an overactive thyroid set off a cascade of complications so rare that clinicians at a Chinese emergency department documented it in detail for the medical literature. A 36-year-old woman receiving methimazole, one of the most widely used drugs for hyperthyroidism, developed agranulocytosis—a near-total loss of infection-fighting neutrophils—and then went on to experience septic shock and an ileocolic intussusception, a condition in which the bowel telescopes into itself. The case, reported by a team at the First Affiliated Hospital of Fujian Medical University in BMC Endocrine Disorders, illustrates how a single adverse drug reaction can spiral into multi-organ failure when the immune system’s first line of defense collapses.

Methimazole is a first-line antithyroid medication that works by blocking the enzyme thyroid peroxidase, thereby curtailing the synthesis of thyroid hormone in patients with autoimmune thyrotoxicosis, most commonly Graves’ disease. The drug is generally well tolerated, but its most feared adverse effect is agranulocytosis, an idiosyncratic hematologic reaction in which the absolute neutrophil count plummets, typically to below 0.5 × 10⁹ per liter. The incidence is low—classically estimated at 0.2 to 0.5 percent of treated patients—but the consequences can be devastating, because neutrophils are the principal cellular effectors of innate immunity against bacteria and fungi. Without them, mucosal barriers in the mouth, throat, and gut become portals for overwhelming infection.

In this case, the patient had been taking methimazole for approximately one month when she presented with fever, pharyngitis, abdominal pain, and diarrhea. The timing is clinically significant: methimazole-induced agranulocytosis most often emerges within the first two to three months of therapy, which is precisely the window in which guidelines recommend vigilance for symptoms such as sore throat and fever. Laboratory evaluation confirmed the severity of her condition, revealing an absolute neutrophil count of just 0.01 × 10⁹ per liter—essentially a complete absence of circulating neutrophils—alongside markedly elevated inflammatory markers indicating a systemic inflammatory response already in progress.

What distinguished this case from the typical presentation of drug-induced agranulocytosis was what imaging revealed next. Computed tomography confirmed an ileocolic intussusception, with the terminal portion of the small intestine having invaginated into the colon. Intussusception is common in infants, where it is usually idiopathic, but in adults it is rare and almost always associated with a pathological lead point such as a polyp, tumor, or—critically in this patient’s situation—disordered motility and inflammatory change driven by severe sepsis. Even more alarming, surgical findings showed transmural necrosis of the involved bowel segment, meaning the intestinal wall had died through its full thickness, a condition that rapidly becomes fatal without resection.

The clinical team faced a genuine dilemma. Emergency surgery in a patient with profound neutropenia and septic shock carries extraordinary risks: the patient has minimal capacity to heal, to fight surgical-site infection, or to withstand the physiological insult of laparotomy. Profound neutropenia has traditionally been regarded as a relative contraindication to major emergency surgery. Yet the authors argue that when septic shock results from intestinal necrosis, the necrotic bowel itself is the source of the sepsis, and no amount of antibiotics will achieve cure without source control. The patient underwent an emergency ileocolic resection with a temporary ileostomy, removing the dead segment and diverting the fecal stream to protect the anastomosis.

Perioperative and postoperative management was aggressively multidisciplinary. The team administered broad-spectrum intravenous antibiotics to cover the gut flora flooding into tissues and bloodstream, and administered granulocyte colony-stimulating factor, or G-CSF, a recombinant growth factor that stimulates the bone marrow to produce and release neutrophils. G-CSF has become standard supportive care in antithyroid drug-induced agranulocytosis, shortening the duration of neutropenia, although its effect on mortality in septic neutropenic patients remains debated. The patient also required multi-organ support in the intensive care unit, reflecting the degree to which septic shock had compromised her cardiovascular and other organ systems.

The authors place their case in the context of a literature review of comparable reports, noting that gastrointestinal complications of agranulocytosis—ranging from necrotizing enterocolitis-like presentations to sepsis-driven bowel perforation—are exceedingly uncommon but well documented. The mechanism they propose for the intussusception is instructive: sepsis and severe inflammation can disrupt normal intestinal peristalsis, creating uncoordinated, spastic bowel contractions. In an adult bowel already weakened by inflammatory injury and mucosal breakdown, these dyskinetic segments can serve as the lead point for telescoping. This reframes intussusception not merely as a mechanical accident but as a potential downstream consequence of systemic immunoparalysis and septic physiology.

The broader lessons of the case concern monitoring and clinical decision-making. The authors emphasize the critical need for vigilant hematologic surveillance in patients starting methimazole, particularly during the first months of therapy. Current practice varies internationally: routine serial white cell counts are not universally recommended because agranulocytosis is unpredictable and idiosyncratic, unrelated to dose in most cases, but all guidelines agree that any patient on antithyroid medication who develops fever or sore throat must have an urgent differential blood count. The message for patients is equally important—symptoms that might suggest an ordinary upper respiratory infection can, in this context, signal a hematologic emergency.

Equally consequential is the paper’s stance on surgery in neutropenic sepsis. By demonstrating a successful outcome after emergency bowel resection in a patient whose neutrophil count was essentially zero, the authors argue that profound neutropenia should not be treated as an absolute contraindication to life-saving source control. The decision framework they describe is one of weighing the mortality of untreated necrotic bowel—approaching certainty—against the substantial but potentially survivable risks of surgery supported by antibiotics, G-CSF, and intensive care. Their conclusion that a multidisciplinary approach involving emergency physicians, endocrinologists, hematologists, surgeons, and intensivists is essential for successful outcomes reflects a growing consensus in the management of complex drug toxicities.

The case also carries a public health dimension. Hyperthyroidism affects a substantial fraction of the population, particularly women, and antithyroid drugs remain the standard initial therapy worldwide, especially in regions where radioactive iodine and surgery are deferred or unavailable. Agranulocytosis, while rare, is a reminder that even familiar, decades-old medications demand respect for their idiosyncratic risks. The Fujian team’s detailed documentation—supported by funding from the Joint Funds for the Innovation of Science and Technology of Fujian Province and approved by their institutional ethics committee with the patient’s written informed consent—adds a valuable data point to a sparse literature, and offers clinicians a template for recognizing and responding to one of the most dangerous intersections of endocrinology, hematology, and emergency surgery.

Subject of Research: Methimazole-induced agranulocytosis complicated by sepsis and ileocolic intussusception

Article Title: Methimazole-induced agranulocytosis complicated by sepsis and ileocolic intussusception: a case report and literature review

Article References: Zhu, X., Zhang, H., Lin, J., Pang, M., Zhang, X., Dong, Y., Huang, Y., & Li, Y. (2026). Methimazole-induced agranulocytosis complicated by sepsis and ileocolic intussusception: a case report and literature review. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-026-02569-4

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02569-4

Keywords: methimazole, agranulocytosis, sepsis, intussusception, hyperthyroidism, adverse drug reaction, G-CSF, neutropenia, thyrotoxicosis, emergency surgery, BMC Endocrine Disorders, case report