How to diagnose generalized weakness on physical examination?

Confirming Generalized Weakness on Physical Examination

To confirm generalized weakness on examination, you must objectively document loss of strength using the Medical Research Council (MRC) Manual Muscle Testing scale, systematically assess the distribution pattern (proximal vs. distal, symmetric vs. asymmetric), and perform a focused neurologic examination including reflexes, cranial nerves, and observation of spontaneous movement quality. 1, 2, 3

Objective Strength Documentation

• Grade muscle strength using the MRC scale (0-5) in multiple muscle groups bilaterally to quantify weakness objectively rather than relying on subjective patient reports 1, 2
• For muscles with MRC grade 3-5, consider quantitative myometry for more precise measurement 1
• Document specific functional deficits: inability to rise from a chair without using arms (proximal lower extremity weakness), difficulty lifting arms overhead (proximal upper extremity weakness), or trouble with fine motor tasks like buttoning (distal weakness) 4, 3

Critical Pattern Recognition

Distribution Assessment

• Proximal weakness (difficulty rising from chair, lifting arms overhead) suggests myopathy, myositis, or inflammatory conditions 4, 3
• Distal weakness (foot drop, hand weakness) suggests peripheral neuropathy 4, 3
• Symmetrical weakness is typical of Guillain-Barré syndrome, ICU-acquired weakness, or metabolic/endocrine causes 4, 2
• Asymmetrical weakness suggests focal nerve lesions, radiculopathy, or stroke 4, 3

Temporal Characteristics

• Fatigable weakness that worsens with sustained activity and improves with rest is highly specific for myasthenia gravis 4, 5
• Rapidly ascending weakness over hours to days suggests Guillain-Barré syndrome 4

Essential Neurologic Survey Components

Reflex Examination

• Preserved or hyperactive reflexes with weakness suggest upper motor neuron pathology (stroke, spinal cord lesion) 5, 2
• Diminished or absent reflexes with weakness suggest lower motor neuron, peripheral nerve, or neuromuscular junction disease 1, 5
• Normal reflexes with fatigable weakness strongly suggest myasthenia gravis 5

Cranial Nerve Assessment

• Evaluate for bilateral ptosis (worse in evening), diplopia, facial weakness, or bulbar symptoms (dysphagia, dysarthria) which indicate myasthenia gravis or brainstem involvement 4, 5
• Test eye movements for vertical gaze palsy (progressive supranuclear palsy) or oculomotor abnormalities 1
• Assess facial expression symmetry and quality of smile/cry 1

Motor Neuron Signs

• Look for fasciculations, muscle atrophy, or tongue wasting suggesting amyotrophic lateral sclerosis 1
• Test for primitive reflexes (grasp reflex) which may indicate upper motor neuron involvement 1

Sensory Examination

• Presence of paresthesias or sensory loss suggests peripheral neuropathy (Guillain-Barré syndrome) rather than neuromuscular junction or primary muscle disease 4, 2
• Absence of sensory findings with weakness points toward myopathy or neuromuscular junction disorders 5, 3

Observation of Spontaneous Movement

• Watch the patient's posture, gait, and spontaneous motor function before formal testing, as stressed examination may not reveal true functional capacity 1
• Observe for parkinsonian features (bradykinesia, rigidity, postural instability) which occur in 25-80% of frontotemporal dementia cases 1
• Note quality and quantity of movement even in uncooperative patients 1

Additional Physical Examination Elements

Respiratory Assessment

• Assess for respiratory compromise (shortness of breath, difficulty breathing) which indicates potentially life-threatening myasthenia gravis crisis or Guillain-Barré syndrome requiring immediate intervention 4
• Bulbar symptoms often precede respiratory failure 4

General Physical Findings

• Measure head circumference, weight, and height with growth curve interpretation, as microcephaly or macrocephaly may suggest underlying genetic or metabolic conditions 1
• Check for muscle wasting (absent in myasthenia gravis, present in muscular dystrophy) 5, 3
• Look for ptosis, facial weakness, or drooling suggesting facial/oral motor weakness 1, 5

Common Pitfalls to Avoid

• Do not confuse subjective fatigue or pain-related motor impairment with true muscle weakness - these require different diagnostic approaches 2, 3
• Do not rely solely on patient history - objective documentation with formal grading scales is essential as history alone led to diagnosis in only 78% of cases in one study 6
• Do not assume normal early examination rules out progressive conditions - repeat examination may be necessary as weakness evolves 1
• Do not overlook medication history - beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and immune checkpoint inhibitors can cause or worsen weakness 4