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

Author

Dr. Shoaib Ahmad Baig
December 31, 2024

🔍 Question of the day

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 Differentials

Differential ⚖️

Why Incorrect? 🔴

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

Stay Hungry, Stay Curious!

Your Brother In This Struggle

Dr. Shoaib Ahmad

ps…Just a heads up!

This is just an excerpt from our high-yield Q bank "Excel USMLE Step1: Respiratory System" that we are launching next month InshaAllah.

With this Q-bank, you’ll be able to Excel any USMLE Step 1 question on respiratory section without fear of getting a wrong answer using our visual charts and flashcards.

This e-book will feature:

  • High-yield USMLE Step 1 questions on the respiratory system.

  • Conceptual clarity for every question to solidify your understanding.

  • Problem-solving strategies to enhance your test-taking skills.

  • Flashcards for each question to reinforce learning.

You can pre-order now.

Future editions covering other systems will follow shortly.

Each e-book in the series is priced individually.

Special Offer:

  • 61% off during the pre-order period.

Money-back guarantee if you’re not satisfied—no questions asked!