Myasthenia Gravis

For myasthenia gravis, there are not so much diagnostic criteria as a set of diagnostic tests with varying sensitivity and specificity. These tests include characteristic clinical course, response to

Table 11

Clinical Classification of Motor Neuron Disorders (Adult Onset, 15-50 Years; Elderly Onset, Over 50 Years)

Disorder

Age at onset

Inheritance

Combined upper and lower motor neuron involvement

Amyotrophic lateral sclerosis Sporadic

Familial adult onset

Familial juvenile onset

Pure lower motor neuron involvement

Proximal hereditary motor neuronopathy Acute infantile form (Werdnig-Hoffmann) Chronic childhood form (Kugelberg-Welander) Adult onset forms

Hereditary bulbar palsy X-linked bulbospinal neuronopathy (Kennedy) With deafness (Brown-Violetta-Van Laere) Without deafness (Fazio-Londe) Hexosaminidase deficiency Multifocal motor neuropathies Postpolio syndrome Postirradiation syndrome

Monomelic, focal, or segmental spinal muscular atrophy Pure upper motor neuron involvement

Primary lateral sclerosis Hereditary spastic paraplegia Neurolathyrism Konzo

Adult, elderly

Adult

Childhood

Infantile

Infantile, childhood Adult

Adult, elderly Childhood, adult Childhood Childhood, adult Adult, elderly Elderly Adult, elderly Adult

Adult, elderly Adult, elderly Adult Adult

Autosomal-dominant Autosomal-recessive

Autosomal-recessive Autosomal-recessive Autosomal-recessive, Autosomal-dominant

Sex-linked-recessive

Autosomal-recessive Autosomal-recessive

Autosomal-recessive

Adapted from Donaghy M. Classification and clinical features of motor neurone diseases and motor neuropathies in adults. J Neurology 1999;246:331-333, with permission from Springer Verlag.

anticholinesterase medications, antibody testing (acetylcholine receptor antibody is the most specific, but only 50% of ocular myasthenics are positive), electromyography (repetitive stimulation and single-fiber electromyogram as appropriate). The differential diagnosis includes other conditions that can produce generalized weakness and/or weakness of ocular muscles. These include Lambert-Eaton myasthenic syndrome, congenital myasthenia, drug-induced myasthenia, hyperthyroidism, Graves' disease, mitochondrial myopathies, motor neuron disease, and central nervous system lesions. There are specific tests for each of these, but it is important to recall that diagnostic testing, such as injection of an anticholinesterase (e.g., Tensilon [edrophonium] testing), may yield false-positives.

In the diagnostic criteria for neuropsychiatry systemic lupus erythematosus (one of many disorders associated with myasthenia gravis), there are diagnostic criteria for myasthenia gravis, but the extent to which the wider medical community or specialists in neuromuscular diseases adhere to this case definition is unclear.

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