Jump to navigation Jump to search

Author Anonymous (Reviewed by Will Gibson, Alison Leibowitz, and Yazan Daaboul)
Exam Type USMLE Step 1
Main Category Behavioral Science/Psychiatry, Pharmacology
Sub Category Neurology
Prompt A 23-year-old woman presents to her primary care physician with complaints of depression, insomnia, and decreased appetite. She reports that these symptoms often alternate with episodes of excited mood and euphoria. The patient is referred to a local psychiatrist for appropriate management. Two months later, the patient returns and reports improvement of her mood swings following daily intake of a medication whose name she cannot recall. She now complains of recent menstrual irregularities, constipation, and fatigue. Which of the following drugs was this patient most likely prescribed?
Answer A Carbamazepine
Answer A Explanation [[AnswerAExp::Carbamazepine is an anticonvulsant and mood-stabilizing drug used primarily for the management of epilepsy and bipolar disorder. It is also the first line treatment for trigeminal neuralgia. Carbamazepine stabilizes the inactivated state of voltage-gated sodium channels, thereby reducing the excitability of neurons. Carbamazepine is an inducer of the cytochrome P-450 system. Adverse reactions to carbamazepine include SIADH, agranulocytosis, aplastic anemia, hepatotoxicity, Stevens-Johnson syndrome, and teratogenicity.]]
Answer B Gabapentin
Answer B Explanation [[AnswerBExp::Gabapentin is a gamma-aminobutyric acid (GABA) analogue that inhibits voltage-gated calcium channels. It is used to treat epilepsy, peripheral neuropathy, and bipolar disorder. Adverse effects include sedation and ataxia.]]
Answer C Venlafaxine
Answer C Explanation [[AnswerCExp::Venlafaxine is an SNRI (inhibits serotonin and norepinephrine reuptake) that may be used to treat depression and generalized anxiety disorder. It may also be used for cases of chronic pain. Classically, venlafaxine is associated with elevations in diastolic blood pressure, nausea, and sedation.]]
Answer D Amitriptyline
Answer D Explanation [[AnswerDExp::Amitryptyline is a tertiary amine tricyclic antidepressant (TCA) that blocks the reuptake of serotonin and norepinephrine. It is primarily used to treat major depression. Adverse effects of amitriptyline include the three C-s: Convulsions, Coma, and Cardiotoxicity. Additionally, TCAs have anticholinergic adverse effects, such as urinary retention, constipation, dryness of the mouth, and sedation. Administration of TCAs is not classically associated with the development of hypothyroidism.]]
Answer E Lithium
Answer E Explanation Lithium is a mood stabilizer used to treat bipolar disorder. Its mechanism of action is poorly understood. Administration of lithium is associated with the development of hypothyroidism, which is responsible for the menstrual irregularities, constipation, and fatigue in this patient. Further questioning might demonstrate other manifestations of hypothyroidism, such as cold intolerance, hair loss, and reduced concentration capacity.
Right Answer E
Explanation [[Explanation::This patient has bipolar disorder and was most likely prescribed lithium for mood stabilization. The mechanism of action of lithium is yet to be elucidated. In bipolar disorder, lithium is indicated for the acute treatment and prophylaxis of mania. Lithium is almost totally excreted in the urine and is associated with the development of tubulo-interstitial nephritis and nephrogenic diabetes insipidus. Other well-established adverse effects of lithium therapy include hypothyroidism, which manifests with fatigue, constipation, and menstrual irregularities as observed in this patient. Lithium has other adverse effects, which can be remembered with the mnemonic LITHIUM:
  • Lethargy / Leucocytosis
  • Intentional tremor
  • Teratogenicity
  • Hypothyroidism
  • Diabetes Insipidus
  • Urine excess (polyuria)
  • Metallic taste

It is important to perform renal and thyroid function tests before the initiation of therapy. Frequent re-assessment is also required to monitor for potential side effects.
Educational Objective: Lithium is a mood stabilizer used to treat bipolar disorder. Administration of lithium is associated with the development of hypothyroidism, which is responsible for the menstrual irregularities, constipation, and fatigue.
References: Bocchetta A, and Loviselli A. Lithium treatment and thyroid abnormalities. Clin Pract Epidemiol Ment Health. 2006;2:23
First Aid 2014 page 518]]

Approved Yes
Keyword Bipolar disorder, Lithium, Hypothyroidism, Adverse effect, Psychiatry, Antipsychotic, Pharmacology, Drug, Mania, Constipation, Fatigue
Linked Question
Order in Linked Questions