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Acute weakness is the acute loss of strength.

  • Bulk: Assess symmetry of muscle bulk

  • Tone: Assess by passive movement of limbs with patient relaxed; may be normal, increased (spastic or rigid), decreased

  • See Table 19-1

TABLE 19-1

Scales for Strength and Deep Tendon Reflexes


  • Central Nervous System (CNS)-Brain: Acute stroke, unilateral or bilateral

  • CNS-Spinal cord (anterior horn cell body): Cord infarction, cord compression, trauma, contusion, infection (e.g., enterovirus), transverse myelitis, spinal epidural abscess, syringomyelia

  • Spinal root of peripheral nerve: Acute inflammatory demyelinating polyneuropathy (Guillain–Barré)

  • Peripheral nerve (axon): Intensive care unit (ICU) neuropathy, HIV or zidovudine therapy, hereditary tyrosinemia, acute intermittent porphyria, medication-related (e.g., phenytoin, vincristine, nitrofurantoin, INH), toxins (heavy metals, glue), metabolic (uremia-mixed sensory and motor, or pure motor after dialysis), autoimmune (lupus), other vasculitis, chronic juvenile rheumatoid arthritis

  • Neuromuscular junction: Myasthenia gravis, botulism, tic paralysis, pharmacologic blockade, aminoglycoside toxicity

  • Muscle: Myositis (infectious, dermatomyositis, polymyositis), metabolic (hypocalcemia, hypokalemia, hypothyroid state), medication-related (especially steroids), ICU myopathy, familial periodic paralysis (hypo/hyperkalemic)


  • Central nervous system: Stroke; typically unilateral weakness in a cerebrovascular distribution; expected concomitant language, cranial nerve, or sensory changes; initial low tone then spastic; extensor plantar response (“upgoing toe”) on affected side (Table 19-2)

  • Spinal cord: Acute flaccid paraparesis (“spinal shock”) then spastic, bowel or bladder symptoms, incontinence, evolving spasticity, sensory level, back pain or trauma, fasciculation, fever (epidural abscess), hypotension (infarction), decreased rectal tone, extensor plantar responses (“upgoing toes”)

  • Spinal root of peripheral nerve: Symmetric length-dependent weakness, often concomitant sensory disturbance, distal more than proximal weakness, areflexia, +/− back pain, normal to decreased tone

  • Peripheral nerve: Weakness and sensory loss in distribution of specific nerve, in several discrete nerve distributions (mononeuritis multiplex), or diffusely in polyneuropathy (may be painful); may have decreased deep tendon reflexes (DTRs)

  • Neuromuscular junction: Hypotonia; DTRs present; no sensory loss (see Myasthenia Gravis and Botulism sections)

  • Muscle: Proximal more than distal weakness; normal tone; myalgias; normal to decreased DTRs

TABLE 19-2

Summary of Examination for Weakness by Localization

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