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AOBNP Neurology & Psychiatry study materials
AOBNP Neurology & Psychiatry study resources

Progressive Weakness in a Patient on a New Medication

AOBNP Neurology & Psychiatry · Put your knowledge to work in context.

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Progressive Weakness in a Patient on a New Medication

A 63-year-old woman presents with 6 weeks of progressive proximal weakness - difficulty rising from a chair, climbing stairs, and lifting her arms overhead. She has hypertension and hyperlipidemia. Medications: atorvastatin 40 mg daily (started 4 months ago), amlodipine, and hydrochlorothiazide. Exam: symmetric proximal weakness (deltoids and hip flexors 4/5), no sensory loss, normal reflexes, no fasciculations, no rash. CK is 2,100 U/L (upper limit of normal ~200). TSH normal. She has no family history of neuromuscular disease and no recent viral illness. She is worried about "ALS" because a friend was recently diagnosed.

1. Construct a differential for proximal weakness with elevated CK and explain which features argue for and against each diagnosis.

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Leading consideration - statin-associated myopathy:

  • Started 4 months ago, temporal relationship fits.
  • Symmetric proximal weakness, CK elevated ~10x upper limit, no rash, no sensory findings.
  • Spectrum ranges from asymptomatic CK elevation to myalgia to true necrotizing autoimmune myopathy (which can persist after statin withdrawal and may require immunosuppression).

Other considerations:

  1. Polymyositis/dermatomyositis - proximal weakness and elevated CK fit; absence of rash argues against dermatomyositis, and the temporal link to a statin makes drug-induced myopathy more likely. Malignancy screening is relevant if inflammatory myopathy is confirmed.
  2. Hypothyroidism - TSH normal, effectively excluded.
  3. Electrolyte/endocrine myopathy - check potassium, magnesium, calcium; hydrochlorothiazide can cause hypokalemia.
  4. Inclusion body myositis - usually older, asymmetric, distal involvement (finger flexors, quadriceps), modest CK; less likely here.
  5. ALS - the patient's fear. Argues against: no upper motor neuron signs, no fasciculations, no bulbar symptoms, normal reflexes, and ALS causes weakness with only mild CK elevation, not 10x. Reassure explicitly.

Judgment being tested: taking the patient's fear seriously while using the exam to exclude it, and not missing a drug cause hiding in the medication list.

2. What is your diagnostic and management sequence, and what would change your approach?

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Sequence:

  1. Stop the atorvastatin (or switch to a non-statin or low-dose alternative) and reassess in 4–6 weeks with repeat CK and exam. This is both diagnostic and therapeutic.
  2. Baseline labs: potassium, magnesium, calcium, TSH (done), aldolase, and consider myositis-specific autoantibodies (anti-HMGCR, anti-SRP) if weakness persists.
  3. EMG/NCS if weakness persists after statin withdrawal or if the diagnosis is unclear - helps distinguish myopathic from neuropathic processes.
  4. Muscle biopsy if autoantibodies are positive or weakness persists despite statin cessation - anti-HMGCR myopathy often requires immunosuppression and does not resolve with drug withdrawal alone.
  5. Address cardiovascular risk - do not leave her without lipid management; consider a non-statin (ezetimibe, PCSK9 inhibitor) or a cautious rechallenge with a different statin at low dose after recovery.

What would change the approach:

  • If CK continues to rise or weakness progresses after stopping the statin → suspect immune-mediated necrotizing myopathy; check anti-HMGCR and involve rheumatology/neurology.
  • If she develops bulbar symptoms, fasciculations, or upper motor neuron signs → urgent neurology referral for ALS evaluation.
  • If she has a rash, mechanic's hands, or interstitial lung symptoms → dermatomyositis/antisynthetase workup.

Judgment being tested: using drug withdrawal as a diagnostic trial, knowing when to escalate to antibodies/biopsy, and not abandoning cardiovascular prevention.

3. She asks whether she can ever take a statin again. How do you answer, and what follow-up do you arrange?

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Answer:

  • Most patients with statin-associated muscle symptoms can tolerate a statin rechallenge, often with a different statin or a lower dose; the risk of recurrence is real but manageable.
  • She should not restart until her CK normalizes and weakness resolves - document a clear timeline.
  • If she has immune-mediated necrotizing myopathy (anti-HMGCR positive), rechallenge is contraindicated and she needs immunosuppressive therapy; this is a distinct diagnosis from simple statin myopathy.
  • Alternatives exist: ezetimibe, PCSK9 inhibitors, bempedoic acid. Her cardiovascular risk should not go untreated.

Follow-up:

  1. Repeat CK and exam in 4–6 weeks.
  2. Lipid panel and cardiovascular risk review at that visit.
  3. If symptoms resolve and CK normalizes, discuss a cautious rechallenge with a different statin at low dose, with instructions to report muscle symptoms promptly.
  4. If weakness persists, arrange neurology referral for EMG and possible biopsy.
  5. Document the adverse reaction clearly in the chart and give her a written summary.

Judgment being tested: balancing the patient's fear of recurrence against the real harm of untreated cardiovascular risk, and distinguishing simple statin myopathy from immune-mediated disease that changes the answer entirely.