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Difficulty: HardAnxiety, OCD, and Trauma-Related Disorders

A 29-year-old woman presents to the psychiatry clinic seeking treatment for new-onset severe anxiety, frequent panic attacks, and irritability that began 2 months ago. She has a history of bipolar II disorder; she was previously treated with valproate but discontinued all medications two years ago and has been stable since. The patient works as a fitness model and notes a 5-kg (11-lb) weight loss over the last 2 months, which she attributes to "burning nervous energy." She feels constantly "on edge" and has been struggling with insomnia. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 135/85 mm Hg, and a heart rate of 112/min. Physical examination reveals a fine tremor of the outstretched hands, brisk deep tendon reflexes, and no palpable thyroid enlargement. An initial laboratory workup is obtained to rule out medical causes of her anxiety:

Laboratory TestResultReference Range
Thyroid-stimulating hormone (TSH)0.02 µU/mL0.4 - 4.0 µU/mL
Free T40.5 ng/dL0.9 - 1.7 ng/dL
Free T36.8 pg/mL2.3 - 4.2 pg/mL

Which of the following is the most appropriate next step in the management of this patient?

  1. Measure serum thyroglobulin concentrationAnswer
  2. B
    Measure thyroid-stimulating immunoglobulin
  3. C
    Initiate levothyroxine therapy
  4. D
    Initiate sertraline therapy
  5. E
    Measure serum thyroid peroxidase antibodies

Answer

Measure serum thyroglobulin concentration
The correct answer is to measure serum thyroglobulin concentration. This patient presents with clinical signs of thyrotoxicosis (anxiety, panic attacks, weight loss, tachycardia, tremor, hyperreflexia) that masquerade as a primary anxiety disorder. Her thyroid panel reveals a suppressed TSH, low Free T4, and elevated Free T3. This specific pattern—low T4 combined with high T3—is highly indicative of exogenous liothyronine (T3) use, a substance sometimes abused for rapid weight loss (e.g., by fitness models). The exogenous T3 suppresses pituitary TSH secretion, which subsequently shuts down endogenous thyroid hormone (T4) production, resulting in the low Free T4 level. To definitively distinguish factitious thyrotoxicosis (exogenous use) from endogenous causes like destructive thyroiditis, a serum thyroglobulin level should be measured. Thyroglobulin is a precursor protein produced by functional thyroid tissue; it will be low (suppressed) in exogenous hormone abuse but elevated in destructive thyroiditis.

Step-by-Step Solution

1
Evaluate the clinical presentation and vital signs.
The patient exhibits severe anxiety, panic attacks, weight loss, tachycardia, and tremor, which strongly suggest a hypermetabolic state such as thyrotoxicosis.
Psychiatric symptoms often have underlying medical etiologies that must be ruled out before making a primary psychiatric diagnosis.
2
Analyze the thyroid function tests.
The panel shows suppressed TSH, low Free T4, and high Free T3.
This specific combination (Low T4, High T3) indicates exogenous T3 (liothyronine) ingestion. The exogenous T3 suppresses pituitary TSH, which in turn halts endogenous T4 production.
3
Determine the best diagnostic test to confirm the etiology.
Select serum thyroglobulin concentration measurement.
Thyroglobulin is produced by active thyroid tissue. It will be low in exogenous hormone abuse due to glandular suppression, but high in endogenous hyperthyroidism or destructive thyroiditis.

Key Concept

Patients presenting with new-onset psychiatric symptoms must be evaluated for medical etiologies; a thyroid profile showing suppressed TSH, low Free T4, and high Free T3 indicates factitious thyrotoxicosis, which is confirmed with a low serum thyroglobulin level.
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Topics

Anxiety, OCD, and Trauma-Related Disorders

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