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Diagnosis of amyotrophic lateral sclerosis and other forms of motor neuron disease

Lauren B Elman, MD
Leo McCluskey, MD, MBE
Section Editor
Jeremy M Shefner, MD, PhD
Deputy Editor
John F Dashe, MD, PhD


Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive, presently incurable, neurodegenerative disorder that causes muscle weakness, disability, and eventually death.

This topic will review the clinical evaluation and laboratory testing needed to support the diagnosis of ALS and other forms of motor neuron disease, as well as the differential diagnosis of ALS. Other aspects of ALS are discussed separately. (See "Clinical features of amyotrophic lateral sclerosis and other forms of motor neuron disease" and "Epidemiology and pathogenesis of amyotrophic lateral sclerosis" and "Familial amyotrophic lateral sclerosis" and "Symptom-based management of amyotrophic lateral sclerosis" and "Disease modifying treatment of amyotrophic lateral sclerosis".)


ALS is one of multiple degenerative motor neuron diseases that are clinically defined, based on the involvement of upper and/or lower motor neurons. ALS is the most common form of motor neuron disease. The diagnosis of ALS is based upon clinical criteria that include the presence of upper motor neuron and lower motor neuron signs, progression of disease, and the absence of an alternative explanation. There is no single diagnostic test that can confirm or entirely exclude the diagnosis of motor neuron disease.

Practically speaking, clinicians make the diagnosis of ALS when it is suggested by the history and physical examination, supported by electrodiagnostic studies, and not excluded by neuroimaging and laboratory studies.

History — The diagnosis of ALS is suggested when there are progressive symptoms consistent with upper and lower motor neuron dysfunction that present in one of four body segments (cranial/bulbar, cervical, thoracic, and lumbosacral) followed by spread to other segments over a period of months to years. The course is not relapsing and remitting, but rather is insidiously progressive. Involuntary weight loss and muscle wasting unrelated to nutrition may also occur.

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Literature review current through: Nov 2017. | This topic last updated: May 18, 2016.
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