Sudden Methimazole Discontinuation and Cough
Stopping methimazole suddenly for surgery does not directly cause cough as a recognized complication. The primary concern with abrupt methimazole discontinuation perioperatively is worsening hyperthyroidism or precipitating thyroid storm, not respiratory symptoms like cough 1, 2.
Understanding the Perioperative Context
When methimazole is stopped before surgery, the main physiological consequence is a rebound increase in thyroid hormone levels, not respiratory symptoms:
Thyroid hormone rebound occurs rapidly: Studies show that when antithyroid drugs are discontinued, serum T4, free T4, and T3 levels increase significantly within days, with T3 rising up to 70-85% above baseline within 2-14 days 3.
Risk of thyroid storm: The abrupt discontinuation of methimazole, particularly in the context of surgical stress, can precipitate thyroid storm—a life-threatening hypermetabolic state characterized by fever, tachycardia, altered mental status, and cardiovascular complications, but not cough 1, 2.
Why Cough is Not a Direct Effect
The evidence does not support cough as a consequence of methimazole withdrawal:
Thyroid storm manifestations: The classic presentation includes fever, tachycardia disproportionate to fever, altered mental status, vomiting, diarrhea, and cardiac arrhythmia—respiratory symptoms like cough are not listed among the diagnostic criteria 1.
Methimazole-related complications: When methimazole causes adverse effects, these typically include hepatotoxicity, agranulocytosis, and multiorgan dysfunction, not isolated respiratory symptoms 4.
Alternative Explanations for Post-Surgical Cough
If cough develops after stopping methimazole perioperatively, consider these more likely causes:
Post-thyroidectomy complications: If the surgery was thyroid-related, cough could indicate laryngeal nerve injury, tracheal irritation, or airway compromise from hematoma 1, 5.
Anesthesia-related causes: Intubation can trigger acute bronchoconstriction, particularly in patients with underlying airway hyperreactivity 1.
Surgical positioning and aspiration: Post-operative cough may result from aspiration, atelectasis, or positioning during surgery 1.
Thyroid enlargement: In rare cases, methimazole can cause goiter formation (through TSH stimulation), which could theoretically cause tracheal compression and cough, but this develops over months, not acutely after discontinuation 6.
Clinical Approach
Focus on the actual perioperative risks of methimazole discontinuation rather than attributing cough to the medication change:
Assess for thyroid storm: Look for fever, tachycardia, agitation, and cardiovascular instability rather than isolated respiratory symptoms 1, 2.
Evaluate surgical complications: If post-thyroidectomy, assess for hematoma using the DESATS approach (Difficulty swallowing, Early warning score increase, Swelling, Anxiety, Tachypnea, Stridor) 5.
Consider standard post-operative causes: Evaluate for aspiration, atelectasis, pulmonary edema, or bronchospasm related to anesthesia 1.
Key Pitfall to Avoid
Do not attribute post-surgical cough to methimazole discontinuation without first excluding more serious and common causes including surgical complications, anesthesia effects, and thyroid storm 1, 5. The evidence consistently shows that methimazole withdrawal causes hormonal changes and potential thyroid storm, not isolated respiratory symptoms.