SAT-608 Severe Exogenous Hyperthyroidism Secondary to Intentional Overdose of Levothyroxine in a Patient with Bipolar Disorder

Abstract

Background: Levothyroxine overdose causing severe exogenous hyperthyroidism is not common. When it does occur, patients should be monitored clinically and biochemically until stable. Case Presentation: A 46 year old Caucasian female with a history of bipolar type 1 disorder was admitted to the psychiatry service with violent behavior and making statements that someone was trying to harm her. She had a past history of Graves’ disease and nine years earlier underwent a total thyroidectomy. She was prescribed levothyroxine and thereafter had a long history of variable compliance. Three months prior to admission her TSH was 186 µIU/mL (0.358-3.74). Levothyroxine was restarted at a dose of 137 mcg once a day and 1 month prior to admission TSH had decreased to 0.15 µIU/mL. At admission she was clinically thyrotoxic with free T4 of >8 ng/dL (0.76-1.46) but the TSH was slightly elevated at 4.86 µIU/mL. She complained of fatigue, intermittent palpitations, irregular menstrual cycles, alternating diarrhea and constipation, anxiety, irritability and agitation but not heat intolerance. Her body weight was stable. Heart rate was 110-120 bpm, no thyroid palpable, no tremors and normal deep tendon reflexes. She was treated with propranolol and levothyroxine was discontinued. On day 3 her TSH was 0.44 µIU/mL with free T4 > 8 ng/dL and free T3 of 21.88 pg/mL (2.18-3.98). Free T4 and free T3 peaked on day 5 with free T4 > 8 ng/dL and free T3 22.27 pg/mL. By day 6 free T4 was 6.52 ng/dL and free T3 20.97 pg/mL and TSH 0.04 µIU/mL. The free T4 and free T3 declined to normal on day 15 while TSH remained suppressed. The patient refused a thyroid scan and RAIU. Her thyroglobulin was low at 0.2 mg/mL (2.8 - 40.9) and TSI was normal < 89% (< 140 % baseline). Initially denying an overdose of levothyroxine, on day 14 she acknowledged that she overdosed with about 10 tablets of levothyroxine just prior to coming to the hospital, after not taking it for several days. Given the extreme elevation of her free T4 and free T3 we believe she overdosed with considerably more than 10 pills of levothyroxine. Inquiries to her pharmacies revealed that she refilled 30 150 mcg Levothyroxine tablets 5 months earlier, 60 137mcg tablets 3 months earlier and 90 150mcg tablets 2 months before admission. Her bipolar disorder was treated with clonazepam and risperidone for mood stabilization. Some of her symptoms of agitation, anxiety and hostility were thought to be partly attributable to thyrotoxicosis. She had clinical improvement of her psychiatric symptoms and was discharged on a dose of 125 mcg levothyroxine daily. Conclusion: Levothyroxine overdose can worsen underlying psychiatric illness. In our case thyroid hormone levels peaked on day 5 and normalized by day 15 after an overdose of levothyroxine.