Question

A 52-year-old woman presents with:

• Symptoms: Gradual-onset leg weakness, difficulty climbing stairs, rising from a chair

• Duration: Several months

• Other details: No chewing issues, bowel/bladder changes, morning stiffness, or joint pain

History:

• Medications: Lisinopril, amlodipine (for hypertension)

• Lifestyle: No tobacco, alcohol, or drug use

Physical Exam:

• Muscle strength: 4/5 in proximal thigh muscles, 5/5 distally

• Tenderness: Mild, proximal thigh

• Deep tendon reflexes: Normal

• Sensory exam: Normal

• Babinski sign: Absent

• Effect of repeated contractions: No change in weakness

Vitals: Normal

Which of the following would establish a diagnosis in this patient?

A Acetylcholine receptor autoantibody test

B. Discontinuation of lisinopril

C. Electromyogram

D. Erythrocyte sedimentation rate

E MRI of the spine

F. Muscle biopsy

G. Serum electrolyte assay

Correct Answer:

F. Muscle biopsy

🧠 Triggers

Idiopathic autoimmune mechanism

Environmental/genetic predisposition

⬇️

Activation of CD8+ T cells ( Immune-mediated Muscle Inflammation)

⬇️

Recognition of autoantigens on myocytes

⬇️
CD8+ T Cells attack muscle fibers
⬇️
Endomysial inflammation (hallmark of polymyositis)
⬇️
🧠 Muscle Fiber Necrosis

Cytokines ↑ (e.g., IL-1, TNF-alpha)

Fibrosis and muscle repair impaired

⬇️
Clinical Manifestations

Proximal muscle weakness (difficulty climbing stairs, standing up)

Mild tenderness (inflammation-induced pain)

Normal reflexes and sensory function (disease affects muscle, not nerves)

⬇️

Definitive Test
⬇️
F. Muscle Biopsy

• Findings:

  • Endomysial inflammation

  • Necrotic muscle fibers

  • Confirms polymyositis diagnosis.

Explanation of Other Answers

A. Acetylcholine receptor autoantibody test (Myasthenia Gravis):

• Fatigable weakness (absent here).

• No muscle tenderness or inflammation.

B. Discontinuation of lisinopril (Drug-induced Myopathy):

• No history of statins or corticosteroids.

• Lisinopril rarely causes myopathy.

C. Electromyogram:

• Helps identify myopathy but lacks specificity compared to biopsy.

D. ESR:

• May be elevated but nonspecific.

E. MRI of the spine:

• Used for structural issues (e.g., radiculopathy).

• Normal reflexes and no radicular pain rule this out.

G. Serum electrolyte assay:

• Electrolyte imbalance (e.g., hypokalemia) causes generalized weakness, not proximal-specific.

Flashcards

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Dr. Shoaib Ahmad

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