Pathophysiology
a group of disorders with progressive upper and lower motor neuron disease causing progressive motor weakness
Signs and Symptoms
1) lower motor neuron signs are symmetric muscle atrophy and fasciculation (rapid and irregular contractions that do not move the limb) 2) upper motor neuron signs are spasticity and hyperreflexia 3) first sign is usually wasting and weakness of hand muscles
Histology/Gross Pathology
1) hallmark is loss of large motor neurons 2) progressive degeneration of anterior horn motor cells accompanied by gliosis 3) loss of myelinated fibers laterally in corticospinal tracts 4) degeneration of motor nuclei in brainstem (especially hypoglossal nuclei, ambiguous and motor trigeminal nuclei 5) degeneration of upper motor neurons of cerebral cortex 6) atrophy of skeletal muscle fibers
Associated Conditions
death occurs from respiratory failure and recurrent bouts of pneumonia (often owing to aspiration)
Inheritance/Epidemiology
1) most common form of motor neuron disease 2) familial – 5% of cases with autosomal dominant inheritance; affected gene (chromosome 21) controls copper-zinc superoxide dismutase 3) duration from onset to death is usually several years 4) worldwide incidence 1/100,000 5) peaks at ages 40-50 years 6) male to female; 2:1
Treatment
1) scattered early anecdotal reports of antibiotic treatment of patients who have improved or stabilized on ceftriaxone and penicillin have led to more in depth studies 2) some experienced ALS neurologists think that ceftriaxone may interact in a beneficial way with select neurotransmitters 3) a minority of physicians think some subsets of ALS may in fact be misdiagnosed Borrelia infection (Lyme disease)
Tips for USMLE
1) lower motor neuron signs are due to loss of anterior horn cells; upper motor neuron signs are due to loss of corticospinal tracts 2) look for a 45-year old auto mechanic who presents with a complaint of constantly dropping his tools from his right hand.
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