Weakness and Paralysis
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Approach to the patient
Weakness is a reduction of power in one or more muscles. Paralysis indicates weakness that is so severe that the muscle cannot be contracted at all, whereas paresis refers to less severe weakness. The prefix hemi- refers to one half of the body, para- to both legs, and quadri- to all four limbs. The suffix -plegia signifies severe weakness or paralysis.
Increased fatigability or limitation in function due to pain or articular stiffness is often confused with weakness by pts. Increased time is sometimes required for full power to be exerted, and this bradykinesia may be misinterpreted as weakness. Severe proprioceptive sensory loss may also lead to complaints of weakness because adequate feedback information about the direction and power of movements is lacking. Finally, apraxia, a disorder of planning and initiating a skilled or learned movement, is sometimes mistaken for weakness.
The history should focus on the tempo of development of weakness, presence of sensory and other neurologic symptoms, medication history, predisposing medical conditions, and family history.
Weakness or paralysis is typically accompanied by other neurologic abnormalities that help to indicate the site of the responsible lesion (Table 53-1). It is important to distinguish weakness arising from disorders of upper motor neurons (i.e., motor neurons in the cerebral cortex and their axons that descend through the subcortical white matter, internal capsule, brainstem, and spinal cord) from disorders of the motor unit (i.e., lower motor neurons in the ventral horn of the spinal cord and their axons in the spinal roots and peripheral nerves, neuromuscular junction, and skeletal muscle).
|Sign||Upper Motor Neuron||Lower Motor Neuron||Myopathic||Psychogenic|
|Distribution of weakness||Pyramidal/regional||Distal/segmental||Proximal||Variable/inconsistent with daily activities|
|Muscle stretch reflexes||Hyperactive||Hypoactive/absent||Normal/hypoactive||Normal|
|Upper Motor Neuron|
|Cortex: Ischemia; hemorrhage; intrinsic mass lesion (primary or metastatic cancer, abscess); extrinsic mass lesion (subdural hematoma); degenerative (amyotrophic lateral sclerosis)|
|Subcortical white matter/internal capsule: Ischemia; hemorrhage; intrinsic mass lesion (primary or metastatic cancer, abscess); immunologic (multiple sclerosis); infectious (progressive multifocal leukoencephalopathy)|
|Brainstem: Ischemia, immunologic (multiple sclerosis)|
|Spinal cord: Extrinsic compression (cervical spondylosis, metastatic cancer, epidural abscess); immunologic (multiple sclerosis, transverse myelitis); infectious (AIDS-associated myelopathy, HTLV-I–associated myelopathy, tabes dorsalis); nutritional deficiency (subacute combined degeneration)|
|Spinal motor neuron: Degenerative (amyotrophic lateral sclerosis), infectious (poliomyelitis)|
|Spinal root: Compressive (degenerative disk disease); immunologic (Guillain-Barré syndrome); infectious (AIDS-associated polyradiculopathy, Lyme disease)|
|Peripheral nerve: Metabolic (diabetes mellitus, uremia, porphyria); toxic (ethanol, heavy metals, many drugs, diphtheria); nutritional (B12 deficiency); inflammatory (polyarteritis nodosa); hereditary (Charcot-Marie-Tooth); immunologic (paraneoplastic, paraproteinemia); infectious (AIDS-associated polyneuropathies and mononeuritis multiplex); compressive (entrapment)|
|Neuromuscular junction: Immunologic (myasthenia gravis); toxic (botulism, aminoglycosides)|
|Muscle: Inflammatory (polymyositis, inclusion body myositis); degenerative (muscular dystrophy); toxic (glucocorticoids, ethanol, AZT); infectious (trichinosis); metabolic (hypothyroid, periodic paralyses); congenital (central core disease)|
|Location of Lesion||Pattern of Weakness||Associated Signs|
|Upper motor neuron|
|Cerebral cortex||Hemiparesis (face and arm predominantly, or leg predominantly)||Hemisensory loss, seizures, homonymous hemianopia or quadrantanopia, aphasia, apraxias, gaze preference|
|Internal capsule||Hemiparesis (face, arm, leg may be equally affected)||Hemisensory deficit; homonymous hemianopia or quadrantanopia|
|Brainstem||Hemiparesis (arm and leg; face may not be involved at all)||Vertigo, nausea and vomiting, ataxia and dysarthria, eye movement abnormalities, cranial nerve dysfunction, altered level of consciousness, Horner’s syndrome|
|Spinal cord||Quadriparesis if midcervical or above||Sensory level; bowel and bladder dysfunction|
|Paraparesis if low cervical or thoracic|
|Hemiparesis below level of lesion (Brown-Séquard)||Contralateral pain/temperature loss below level of lesion|
|Spinal motor neuron||Diffuse weakness, may involve control of speech and swallowing||Muscle fasciculations and atrophy; no sensory loss|
|Spinal root||Radicular pattern of weakness||Dermatomal sensory loss; radicular pain common with compressive lesions|
|Polyneuropathy||Distal weakness, usually feet more than hands; usually symmetric||Distal sensory loss, usually feet more than hands|
|Mononeuropathy||Weakness in distribution of single nerve||Sensory loss in distribution of single nerve|
|Neuromuscular junction||Fatigable weakness, usually with ocular involvement producing diplopia and ptosis||No sensory loss; no reflex changes|
|Muscle||Proximal weakness||No sensory loss; diminished reflexes only when severe; may have muscle tenderness|
An algorithm for the initial workup of weakness is shown in Fig. 53-1.