Weakness

Authors: Flaherty, Alice W.; Rost, Natalia S.

Title: Massachusetts General Hospital Handbook of Neurology, The, 2nd Edition

Copyright 2007 Lippincott Williams & Wilkins

> Table of Contents > Child Neurology > Weakness

Weakness

A. See also

Adult Neuromuscular Disorders, p. 80, Adult Weakness, p. 129. The following focuses on static or progressive weakness. Acute weakness suggests vascular event or trauma. Subacute weakness suggests tumor, infection. If onset was prenatal, there is often arthrogryposis, dislocated hips.

B. Hypertonia vs. hypotonia

• Hypertonic infants: From CNS damage. May be hypotonic first.

  • Static hypertonia: Usually cerebral palsy or a perinatal event.

  • Progressive hypertonia: Can be a mass lesion or metabolic dz.

• Hypotonic infants: From CNS trauma or vascular lesions, genetic dz, mitochondrial dz, congenital hypomyelination syndrome, myasthenia, benign central hypotonia, spinal muscular atrophy, congenital myopathies and dystrophies. Specific causes discussed below.

C. Upper motor neuron hypotonia

See Developmental delay, p. 132. CNS hypotonia in infants usually has decreased tone with relatively preserved strength, in contrast to peripheral causes. CNS hypotonia progresses to hypertonia and spasticity.

D. Lower motor neuron dz

• H&P: Weakness, hypotonia, areflexia, fasciculations.

• Tests: CPK, NCS, EMG; consider genetic tests, e.g., for spinal muscular atrophy.

• DDx:

  • NCS normal:

    • Acute: Polio, Coxsackie, echoviruses.

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    • Chronic: Pure anterior horn cell sx suggest spinal muscular atrophies. Additional lethargy suggests organic acidurias. Glycogen on muscle biopsy suggests Pompe's dz.

  • NCS very slow: Do sural nerve biopsy; consider congenital hypomyelinating neuropathy, neuroaxonal dystrophy, infantile neuronal degeneration.

E. Spinal cord damage

• H&P: Difficult or breech delivery, sensory level, sphincter disturbance.

• Causes: Trauma can present with hypotonia in newborns. Also consider tumor, hypoxic myelopathy.

  • Atlantoaxial dislocation: From dislocation of C1-2. Presents as acute or slowly progressive quadriplegia.

  • Meningocele or spina bifida: see p. 135.

  • Occult spinal dysraphism: AKA tethered cord syndrome, spina bifida occulta.

    • H&P: Pts present with back pain, bladder trouble, distal weakness or numbness, hemiatrophy, or scoliosis. Look for sacral dimple or lipoma, brisk leg reflexes.

    • Tests: MRI shows a low-lying conus. A conus below L2-3 is always abnormal in children over 5.

    • Rx: Surgery (controversial).

  • Syringomyelia: See Sensory Loss, p. 111.

F. Peripheral weakness

Pts. are hyporeflexic with normal mental status.

• Peripheral neuropathy: Toxic, metabolic, traumatic (e.g., brachial plexus injuries, p. 94), Guillain-Barr syndrome, infectious, congenital hypomyelination syndrome, Charot-Marie-Tooth dz (types 1, 2, 4).

• Neuromuscular junction (NMJ) dz:

  • Botulism: Infants can get botulism from honey.

  • Myasthenia: Two types:

    • Neonatal: Via transplacental IgG; resolves with time.

    • Congenital: Genetic dz of NMJ; does not resolve with time.

• Myopathy:

  • H&P: Proximal > distal weakness, reflex loss proportional to weakness, muscle pain, steppage gait, waddle, trouble rising from floor, Gower's sign ( walking hands up thighs to help straighten torso), atrophy, contractures, sometimes myotonia, family history.

  • Tests: CPK, EMG/NCS, muscle biopsy.

  • DDx:

    • CPK markedly high:

      • Inflammatory changes on biopsy: Dermatomyositis or polymyositis. Gradual onset of weakness, malaise, muscle pain, fever, rash, edema. May cause GI ulcers or infarcts. Treat with high-dose steroids.

      • Muscle biopsy dystrophic: Muscular dystrophy.

        • Duchenne's: Most common. X-linked dystrophin deletion, with onset < age 5, proximal weakness, cardiac and GI involvement.

        • Becker's: Dystrophin alteration, onset > age 5, milder. Early rx with steroids can slow progression.

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        • Merosin: Congenital dystrophies have merosin-positive, primary merosin-deficient, and secondary merosin-deficient forms.

    • CPK normal or mildly high:

      • Myopathy on EMG and biopsy:

        • Shoulder and hip weakness worst: Endocrine, genetic, or metabolic myopathies, limb-girdle dystrophy.

        • Other muscles involved early: Dystrophies (fascioscapulohumeral, Emery-Dreyfuss, oculopharyngeal).

      • Myotonia present: Myotonic dystrophy (not present in infants), myotonia congenita, paramyotonia.

      • Congenital myopathies: Central core, central nuclear, and nemaline (rod) myopathies.

      • Muscle weakness is intermittent: Hypo- or hyperkalemic periodic paralysis, deficiency of phosphorylase, carnitine-palmital transferase, or phosphofructokinase.

      • Endocrine causes: Myopathy from thyroid, parathyroid, or adrenal abnormalities (either hyper or hypo).

      • Rx: Treat specific cause; close respiratory and cardiac follow-up, scoliosis screening.

G. Genetic disorders causing, initially, weakness alone

Adrenoleukodystrophy, familial spastic paraplegia (a variant of spinocerebellar degeneration), spinomuscular atrophies, Charcot-Marie-Tooth dz, muscular dystrophies, metabolic myopathies, Prader-Willi dz.

H. Benign central hypotonia

Usually mild, often with some gross motor delay. Dx of exclusion.