Weakness

Chapter 42 Weakness



Adam Hartman




ETIOLOGY



What Causes Weakness in Infants and Children?


The differential diagnosis may be approached anatomically (i.e., cerebral hemispheres, spinal cord, and neuromuscular junction) or temporally (i.e., prenatal exposures to toxins, postnatal infections). The emphasis in this section is anatomic diagnosis. Table 42-1 lists the causes of weakness by anatomic location.


Table 42-1 Etiology of Weakness by Anatomic Location













































































Systemic
Endocrine (thyroid parathyroid, adrenal)
Heavy metal intoxication
Sepsis
Inborn errors of metabolism (maple syrup urine disease, glycogen storage disease, type II)
Cerebral Hemispheres and Cerebellum
Cerebral palsy (especially extrapyramidal)
Migrational abnormalities
Cerebral malformations (e.g., schizencephaly)
Benign congenital hypotonia
Chromosomal abnormalities (e.g., trisomy 21, Prader-Willi syndrome)
Stroke
Spinal Cord
Spinal muscular atrophy, types 1–3
Occult dysraphism
Trauma
Poliomyelitis
Transverse myelitis
Spinal cord tumors or abscesses
Peripheral Nerve
Hereditary peripheral neuropathies
Guillain-Barré syndrome
Refsum disease
Bell’s palsy
Trauma
Critical illness polyneuropathy
Neuromuscular Junction
Myasthenia (neonatal, congenital, and juvenile forms)
Eaton-Lambert syndrome
Botulism
Aminoglycoside antibiotics (usually in combination with other disease processes)
Muscle
Muscular dystrophy
Myotonic dystrophy
Congenital myopathies
Metabolic myopathies (including storage disorders, mitochondrial diseases, periodic paralyses, and iatrogenic)
Inflammatory myopathies (including dermatomyositis)


What Causes Muscular Dystrophy?


Muscular dystrophy (MD) is a group of disorders involving different muscle proteins. Duchenne MD is an X-linked recessive disorder that results from a deficiency of dystrophin. It usually presents in males in the first decade and progresses to respiratory failure in the second or third decade. Becker MD becomes clinically apparent in the first or second decade and is a milder form of X-linked dystrophin abnormality. Facioscapulohumeral MD is an autosomal dominant disorder with findings of facial weakness, winged scapulae, and lower limb weakness after the first decade. Limb-girdle MD is a family of disorders caused by abnormalities of sarcolemmal membrane proteins that has autosomal recessive or dominant inheritance. Symptoms appear in the first or second decade with slow disease progression.



What Causes Spinal Muscular Atrophy?


Spinal muscular atrophy (SMA) is the most common fatal neuromuscular disease of infancy. The three clinical forms all represent a deficiency of the SMN1 gene (survival motor neuron 1) on chromosome 5, which produces the SMN protein. An identical gene, SMN2, also produces SMN protein but not as effectively as SMN1. Hence, the clinical forms of SMA represent variable production of functional SMN from the SMN2 locus. Patients with certain forms of SMA may have extra copies of SMN2. All forms of SMA involve atrophy of the anterior horn cells. Type 1, also known as Werdnig-Hoffman disease, has its onset early in infancy. Affected children rarely survive the first year of life. Infants affected with type 2 develop abnormalities after 6 months of life and have a slower progression of disease. Type 3, also known as Kugelberg-Welander disease, usually appears only after 18 months and has a very slow disease progression.



What Is Guillain-Barré Syndrome?


Guillain-Barré syndrome (GBS) is a polyneuropathy with acute ascending weakness, areflexia, paresthesias and/or dysesthesias, and autonomic dysfunction. Symptoms typically plateau over the course of a few weeks. One motor form of the disease has been associated with Campylobacter jejuni infection. A variant, known as Miller-Fisher syndrome, consists of ataxia, ophthalmoplegia, and areflexia. The differential diagnosis of GBS includes botulism, transverse myelitis, myasthenia gravis, spinal cord trauma, toxin ingestion, inflammatory and metabolic myopathies, and tick paralysis.



How Does Botulism Present at Different Ages?


Infant botulism is the result of botulinum toxin expressed by ingested spores, whereas botulism in older children and adults is because of ingestion of the toxin itself. Infants typically present with constipation and weakness; cranial nerve dysfunction and hyporeflexia may appear later. Infant botulism is more common in Pennsylvania, Utah, and California. Older children and adults more commonly present with bulbar symptoms (e.g., cranial nerve abnormalities) and descending weakness.



EVALUATION



How Do I Know Whether an Infant Is Floppy?


An infant is floppy if decreased tone or muscle strength is evident on examination. Easy fatigability and joint laxity may also be seen. The infant may have a significant head lag, may have a positive “slip-through” test in vertical suspension, or may be easily draped over the examiner’s hand when examined in the prone position (horizontal suspension).

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Jun 19, 2016 | Posted by in PEDIATRICS | Comments Off on Weakness

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