Thyrotoxicosis in a 32-Year-Old Female on Levothyroxine Therapy

Case at a Glance

A 32-year-old female with a history of hypothyroidism on levothyroxine replacement therapy presented with clinical signs and symptoms suggestive of thyrotoxicosis, including tachycardia, tremor, polyphagia, and polydipsia.

Patient's Story

The patient reported a constellation of symptoms concerning for hyperthyroid state, including excessive hunger, increased thirst, generalized weakness, and bilateral hand tremors. She was particularly concerned about her elevated resting heart rate of 130 beats per minute. Her current medications included levothyroxine 150 mcg daily for hypothyroidism, duloxetine 60 mg daily for mood disorder, and buspirone 10 mg three times daily for anxiety management.

Initial Assessment

Clinical presentation was consistent with thyrotoxicosis in a patient on thyroid hormone replacement therapy. The patient exhibited classic symptoms including tachycardia (resting HR 130 bpm), tremor, polyphagia, polydipsia, and weakness. Differential diagnosis included levothyroxine overreplacement, medication non-compliance leading to erratic dosing, or underlying thyroid pathology.

The Diagnostic Journey

The case required urgent but non-emergent evaluation. Primary care consultation was recommended over emergency department presentation, as the patient's symptoms, while concerning, did not indicate thyroid storm or other life-threatening complications. Thyroid function tests including TSH, free T4, and free T3 would be essential for diagnosis confirmation.

Final Diagnosis

Probable iatrogenic thyrotoxicosis secondary to levothyroxine overreplacement therapy, pending laboratory confirmation with thyroid function studies.

Treatment Plan

Immediate management included dose reduction of levothyroxine by approximately 25 mcg daily (achieved by skipping one 150 mcg tablet weekly). Close monitoring with primary care physician was recommended rather than emergency department evaluation. Symptomatic management of tachycardia and tremor could be considered if symptoms persisted.

Outcome and Follow-up

Patient was advised that therapeutic response would require 6 weeks to reach steady state after dose adjustment. Regular monitoring of thyroid function tests and clinical symptoms was planned, with further dose titration as indicated by laboratory results and clinical response.