Common causes of weakness
Weakness (reduced muscle power) results from dysfunction at any level of the motor pathway — brain, spinal cord, peripheral nerve, neuromuscular junction or muscle. Stroke produces sudden, usually asymmetric weakness with limb involvement and may include facial droop, speech difficulty or visual loss. Peripheral neuropathy causes weakness in a length-dependent pattern, often with sensory change. Neuromuscular junction disorders (myasthenia gravis) produce fluctuating weakness that worsens with activity and improves with rest. Myopathies (inflammatory, metabolic) cause proximal weakness — difficulty rising from a chair, climbing stairs or lifting objects overhead.
The pattern of weakness provides diagnostic clues: sudden onset suggests stroke; fluctuating weakness suggests myasthenia gravis; proximal weakness suggests myopathy; distal weakness with sensory change suggests neuropathy. History maps onset (acute vs gradual), distribution (proximal vs distal, symmetric vs asymmetric), fluctuation (fatigable vs constant) and associated features (numbness, pain, bulbar symptoms, double vision).
- Stroke — sudden, asymmetric, with facial or speech signs
- Neuropathy — distal, length-dependent, with sensory change
- Myasthenia gravis — fluctuating, fatigable, improves with rest
- Myopathy — proximal, difficulty with stairs or rising from chair
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What evaluation includes
Evaluation begins with detailed history of weakness onset, distribution, progression, associated features and functional impact. Neurological examination assesses power (MRC grading), tone, reflexes, coordination, gait and cranial nerves. Red flags — sudden onset, respiratory difficulty, bulbar symptoms (difficulty swallowing or speaking) — prompt urgent escalation.
Investigations are targeted to the suspected level of the motor pathway. Nerve conduction studies (NCS/EMG) help distinguish neuropathy from neuromuscular junction or muscle disease. Blood tests may include creatine kinase (CK) for myopathy, thyroid function, inflammatory markers and specific antibodies (AChR, MuSK for myasthenia gravis). MRI of brain or spine is considered when central causes are suspected. The clinic focuses on reversible contributors and avoids reflexive investigation.
- Motor pathway assessment — brain, spinal cord, nerve, junction, muscle
- NCS/EMG for neuropathy vs neuromuscular junction vs myopathy
- Blood tests: CK, thyroid, inflammatory markers, specific antibodies
- MRI when central causes are suspected