How do you confirm weakness through examination?

Confirming Muscle Weakness Through Clinical Examination

Manual muscle testing (MMT) using the Medical Research Council (MRC) scale is the most reliable and standardized method to objectively confirm weakness during physical examination, with an MRC score below 80% of maximum (or <4/5 in individual muscle groups) indicating significant weakness. 1

Systematic Approach to Muscle Strength Assessment

Step 1: Differentiate True Weakness from Other Symptoms

• First distinguish true muscle weakness from subjective fatigue, pain-related motor impairment, or asthenia 2
• Ask specific questions about functional limitations:
  • "Is there anything your child is not doing that you think they should be able to do?" (for pediatric patients) 1
  • "Is there anything you used to be able to do that you can no longer do?" (regression of abilities) 1

Step 2: Perform Objective Strength Testing

• Use the MRC scale for grading muscle strength (0-5 scale):
  • 0: No contraction
  • 1: Visible contraction but no movement
  • 2: Movement with gravity eliminated
  • 3: Movement against gravity
  • 4: Movement against resistance (but weaker than normal)
  • 5: Normal strength 3
• Test key muscle groups bilaterally for comparison:
  • Upper extremities: Shoulder abduction, elbow flexion/extension, wrist flexion/extension, grip strength, finger abduction
  • Lower extremities: Hip flexion/extension, knee flexion/extension, ankle dorsiflexion/plantar flexion 1
• For quantitative measurement, use:
  • Grip and pinch dynamometry (provides normative data for comparison) 1
  • Motricity Index for stroke patients (tests 3 key segments in upper and lower extremities) 1

Step 3: Observe Functional Strength

• For uncooperative patients (especially children and toddlers):
  • Observe quality and quantity of spontaneous movement
  • Note antigravity movements in infants
  • Observe transitions from sitting to standing, walking, running, climbing 1
• Watch for specific signs:
  • Gower maneuver (using arms to push up from floor) suggests proximal weakness 1
  • Unsteady gait or tremor may indicate muscle weakness 1
  • Drooling or poor weight gain may suggest facial/oral motor weakness 1

Step 4: Evaluate Pattern of Weakness

• Determine distribution:
  • Proximal vs. distal
  • Symmetric vs. asymmetric (asymmetry more common in neurologic conditions) 2
  • Focal vs. generalized
• Assess for associated findings:
  • Muscle atrophy or hypertrophy
  • Abnormal tone (spasticity, rigidity, hypotonia)
  • Deep tendon reflexes (hyper- or hyporeflexia)
  • Sensory deficits 1

Additional Diagnostic Considerations

Laboratory Testing

• Initial laboratory evaluation should include:
  • Complete metabolic panel and electrolytes
  • Complete blood count
  • Thyroid function tests (TSH, free T4)
  • Creatine kinase (CK) for suspected myopathy 4
  • Vitamin B12 levels 4

Advanced Testing

• Electromyography (EMG) and nerve conduction studies (NCS) if:
  • Weakness persists after initial evaluation
  • Diagnosis remains unclear after clinical examination
  • Suspected conditions include ALS, myasthenia gravis, neuropathy, or radiculopathy 1, 2
• MRI indicated for:
  • Acute neurologic conditions (stroke, cauda equina syndrome)
  • To guide muscle biopsy 2

Common Pitfalls to Avoid

• Failing to distinguish true weakness from fatigue or pain-limited effort
• Not testing strength against resistance (many conditions only manifest with resistance testing)
• Overlooking subtle asymmetry in strength
• Missing proximal weakness by only testing distal muscle groups
• Neglecting to assess for sensory deficits that may accompany weakness
• Relying solely on patient self-report rather than objective testing 5

By following this systematic approach, clinicians can accurately confirm the presence of weakness, characterize its pattern, and guide appropriate further diagnostic evaluation to determine the underlying cause.