Review Question - QID 108956

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Porphyria Cutanea Tarda Treatment Avoid exposures (alcohol, estrogen, primidone, other hepatotoxins) QID: 108956 (M2.DM.17.4754)

QID 108956 (Type "108956" in App Search)

A 36-year-old female presents to her primary care provider for tremor. She reports that she has always had a mild tremor but that she has begun noticing it more since learning to paint. She feels that she has trouble dipping her paintbrush in the paint and making precise strokes on the canvas. She has taken to painting while drinking wine, as she notices that the wine seems to improve her tremor. Her temperature is 97.6°F (36.4°C), blood pressure is 105/61 mmHg, pulse is 58/min, and respirations are 12/min. On exam, she has a high frequency bilateral hand tremor elicited on finger-to-nose testing. Her neurological exam is otherwise unremarkable. The patient is started on a new medication for her symptoms. One week later, she returns with a new complaint of abdominal pain for one day. She reports that she has noticed a darkening of her urine and now has difficulty raising her arms over her head to brush her hair.

This patient was most likely treated with which of the following medications?

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Topiramate

16%

11/68

Propranolol

28%

19/68

Primidone

49%

33/68

Alprazolam

3/68

Clozapine

1/68

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This patient initially presents with classic symptoms of essential tremor and then returns after treatment with abdominal pain, dark urine, and proximal muscle weakness, which suggest a diagnosis of acute intermittent porphyria. Acute intermittent porphyria is known to be triggered by primidone.

An essential tremor is usually a bilateral hand tremor, as in this patient, but could also present as an isolated head tremor. The tremor classically worsens with action, particularly fine motor movements, and is relieved by alcohol. The first-line treatment for essential tremor is propranolol, but its use was contraindicated in this patient in light of her bradycardia. Alternatives include primidone and topiramate, but only primidone is known to precipitate an episode of acute intermittent porphyria (AIP) via it's metabolite phenobarbital.

Incorrect Answers:
Answer 1: Topiramate is an antiepileptic that may be used to treat essential tremor (ET). It can cause the side effects of weight loss and memory loss, but it is not known to trigger acute intermittent porphyria (AIP).

Answer 2: Propranolol is a first-line medication for ET but would have been contraindicated in this patient due to her bradycardia. It is also not known to cause AIP.

Answer 4: Alprazolam is a benzodiazepine that is sometimes used to treat ET. It can cause ataxia or slurred speech, but it would not precipitate an episode of AIP.

Answer 5: Clozapine is atypical antipsychotic that is uncommonly used to treat ET. It can lead to the important adverse event of severe agranulocytosis. It has not been shown to precipitate AIP.

Bullet Summary:
Phenobarbital is a metabolite of primidone and can exacerbate acute intermittent porphyria.

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