🧠 “Why Can’t I Move My Arm?” — A Family Doctor’s Guide to Diagnosing Motor Paralysis

What You’ll Learn

• How to construct a problem list using semantic qualifiers
• How to examine motor/sensory deficits for lesion localization
• How to identify red flags and distinguish common vs rare causes

Clinical Vignette

Patient: 70-year-old male
Chief Complaint: “I can’t move my right hand”
Vitals: BP 140/88, HR 84, Temp 36.7°C, SpO₂ 97%

“I woke up this morning and couldn’t move my right hand. It feels weak, and there’s a bit of numbness too… What’s happening to me?”

Initial Impression

We often feel lost with neurologic symptoms, but one powerful approach is to use two parallel processes:

1. Create a problem list based on patient history
2. Create another based on neurological physical findings

Three key early questions:

• Central (brain/spinal) or peripheral lesion?
• Acute vs chronic? Fixed vs progressive?
• Isolated motor, or accompanied by sensory/speech issues?

Think red flags early: stroke, spinal cord compression, acute demyelination.

Fact → Problem → Hypothesis

• Fact: Woke up with right upper limb weakness. Mild numbness. Speech and consciousness intact.
• Problem: Acute, fixed motor paralysis in right upper limb with mild sensory symptoms. No signs of stroke or GBS.
• Hypotheses: Vascular (stroke), radiculopathy, cervical myelopathy, inflammatory neuropathy, metabolic causes (electrolytes, thyroid).

VITAMIN C-based Differential:

• Vascular: Lacunar infarct, embolism
• Inflammatory: GBS, CIDP
• Trauma: Disc herniation, nerve root injury
• Neoplasm: Spinal tumor
• Congenital: AV malformation

Step 1: History Taking

OPQRST

• O: When did it start? Sudden vs gradual?
• P: Better/worse with posture or movement?
• Q: Weakness, heaviness, numbness, tingling?
• R: Localized to one limb? Radiating?
• S: Severity—can they hold a cup, button a shirt?
• T: Has it improved, worsened, or stayed the same?

PAM HITS FOSS

• Past History: Stroke, DM, malignancy
• Allergy: Vaccine or drug-induced neuro symptoms?
• Medications: Statins, chemo, immunosuppressants
• Injury/Surgery: Especially spinal/neck procedures
• Social/Sexual History: HIV, STI risk, alcohol, lead exposure

Step 2: Physical Exam

Key goal: Localize the lesion

• Strength: Deltoid, biceps, triceps, wrist flexors
• Reflexes: Biceps, triceps, Babinski
• Sensation: C5–C6 dermatomes
• Coordination: Finger-to-nose, gait
• Cranial Nerves: CN II–XII

Example Documentation

MMT: Right deltoid 5/5, biceps 3/5, triceps 3/5
Reflex: Biceps 1+, Babinski flexor bilaterally
Sensation: ↓ light touch, C5–C6 dermatomes
Cranial Nerves: Intact
  

Step 3: Investigations

Blood Tests

• CBC, CRP, electrolytes (Na, K, Ca, Mg)
• Thyroid panel (TSH, FT4), cortisol/ACTH
• CK, HbA1c, B12, folate, copper
• Infectious: HIV, syphilis, HSV, HTLV-1

Imaging

• CT head (to exclude bleed)
• MRI brain and cervical spine
• EMG/Nerve conduction study
• CSF analysis if needed

Example: CT: negative, MRI: C5/C6 disc herniation, NCS: confirms radiculopathy → Diagnosis: Right C6 radiculopathy

Clinical Reflection

“So the patient has sudden right upper limb weakness. No speech issues, no fever, no trauma… that already helps narrow things.”

“On exam, there’s decreased strength in biceps and triceps. Reflexes are slightly diminished too, and sensation loss is in the C5–C6 area. Hmm… that matches a cervical nerve root pattern.”

“No Babinski or other signs of upper motor neuron issues. That makes spinal cord myelopathy less likely.”

“His MRI shows a disc herniation at C5/C6, and the nerve conduction study confirms root involvement. That’s consistent.”

“It’s not a stroke, not GBS, and not systemic. I feel pretty confident calling this a right C6 radiculopathy.”

Clinical Pearls

“When you hear hoofbeats, think horses, not zebras.” – Theodore Woodward, M.D.

Always rule out common causes like stroke and cervical radiculopathy before diving into rarer diagnoses.

“Neurology is not about knowing all diseases—it’s about localizing the lesion.” – Neurology proverb

Focus on where the problem lies, not just what disease it might be.

Useful Medical Expressions

• “Can you tell me exactly what part of your arm feels weak?”
• “Is it just weakness, or do you also feel numbness or tingling?”
• “He has flaccid paralysis of the right upper limb.”
• “The deep tendon reflexes are diminished on the affected side.”

Layman’s Terms & Idioms

• “It feels dull or tingly.” = numbness
• “The nerve in your neck may be getting pinched.” = radiculopathy
• “I can’t really feel when something touches me.” = sensory deficit

Medical English Insights

• Paralysis: complete loss of muscle function
• Paresis: partial weakness
• Radiculopathy (US) = nerve root entrapment (UK)
• Tingling, pins and needles: common patient expressions for sensory symptoms

USMLE High-Yield Topics

• Stroke Syndromes: differentiate cortical, lacunar, brainstem strokes
• Upper vs Lower Motor Neuron signs: reflexes, tone, Babinski
• GBS vs CIDP: acute vs chronic, CSF findings
• Myasthenia Gravis: fluctuation, ptosis, edrophonium test
• Spinal cord compression: red flags, need for MRI

Mnemonics

• VITAMIN CDE – Vascular, Infectious/Inflammatory, Trauma, Autoimmune, Metabolic, Idiopathic, Neoplasm, Congenital, Degenerative, Endocrine
• SPINE – Sudden onset, Progression, Involvement (motor/sensory/autonomic), Neuro level, Emergency signs

Column: Stroke Mimics – Don’t Miss Cervical Radiculopathy

While sudden limb weakness often raises concern for stroke, always consider mimics. Cervical radiculopathy can present with unilateral weakness and sensory changes, especially without central signs like facial droop or dysarthria. Careful mapping of symptoms to dermatomes and use of MRI can prevent misdiagnosis.

Further Reading

• UpToDate: “Approach to the patient with peripheral neuropathy”
• Preston & Shapiro: Electromyography and Neuromuscular Disorders (Elsevier)
• DeMyer’s Techniques of the Neurologic Examination (McGraw-Hill)

References

1. DeMyer W. Techniques of the Neurologic Examination. McGraw-Hill; 2004.
2. Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders. Elsevier; 2020.
3. 日本神経学会. 神経学の進歩 第63巻, 2019.
4. 日本糖尿病学会. 糖尿病診療ガイドライン 2023.
5. UpToDate: “Approach to the patient with peripheral neuropathy”

Tips

• Ask patients to show the weakness
• Clarify what “weak” means—loss of strength vs strange sensation
• Map symptoms to dermatomes or myotomes
• Look for asymmetry and distribution
• Use Problem List format to summarize findings