A Diagnostic Dilemma of Abnormal Thyroid Labs Concerning for Hyperthyroidism in a Patient with Serotonin Syndrome

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 449-497-Thyroid Neoplasia & Case Reports
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-451
Carly E Kelley*1, Lillian Frances Lien2 and Jennifer Marie Perkins1
1Duke University Medical Center, Durham, NC, 2Duke Univ Med Center, Durham, NC
Background:  The clinical presentation of serotonin syndrome may be similar to hyperthyroidism.

Clinical Case:  A 68-year man with bipolar and obsessive-compulsive disorder was found down at home by his sister. Prior to admission, the patient’s mental status had become increasingly altered with signs of mania over the preceding weeks.  He had taken psychiatric medications in the past including fluoxetine.  Head CT was negative. His temperature was 38.5 C. Vital signs were stable with a pulse of 80. Skin was warm and moist; neck was supple without thyromegaly; no lid lag or exopthalmos. Bowel sounds were hyperactive. He was hyper-reflexive with increased tone and 4-5 beats of inducible clonus. Labs revealed:  WBC 18.8 x 10^9 (3.2-9.8), AST 174 U/L (15-41), ALT 57 U/L (17-63), CK 6169 U/L (30-220), sedimentation rate of 65 MM@1hr (0-15), C Reactive Protein of 16.14 mg/dL (<0.60),  urine drug screen positive for benzodiazepines and opioids, negative acute hepatitis panel.  Urinalysis, Chest XRAY, and lumbar puncture showed no signs of infection. Additionally, TSH was 0.02 uIU/mL (0.34-5.66) and free T4 was 2.05 ng/dL (0.52-1.21). He had no history of thyroid disease.

He was admitted for serotonin syndrome in the setting of presumed fluoxetine overdose with potential co-ingestion of other selective serotonin reuptake inhibitors.  He was also empirically started on a beta blocker given his abnormal thyroid labs. Repeat TSH was 1.53 uIU/mL with free T4 of 1.84 ng/dL, free T3 of 2.10 pg/mL (2.20-3.80), and negative TRab. Thyroxine binding globulin was 15. The next TSH was 0.81 ng/dL with a free T4 of 1.28 ng/dL. The patient’s condition stabilized quickly and he was discharged once psychiatrically stable.

He presented again 1.5 months later in a myxedema state with TSH of 75 uIU/mL and undetectable free T4. He was started on IV levothyroxine and his condition improved. Antimicrosomal antibodies were negative.

Discussion:  Thyroid labs may not easily distinguish between serotonin syndrome and hyperthyroidism for several reasons:  in the setting of severely increased serotonin, non-thyroidal illness syndrome (NTIS) is a possibility, and thyroid assay precision may also be an issue. Besides NTIS, the patient’s labs could also be consistent with a resolving thyroiditis, as supported by his later presentation with overt hypothyroidism. In such cases, close outpatient follow-up of thyroid labs must be emphasized.

Nothing to Disclose: CEK, LFL, JMP

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