Amyotrophic Lateral Sclerosis Diagnostics

Laboratory Tests and Ancillaries

Laboratory Studies  

Essential blood tests in the diagnosis of amyotrophic lateral sclerosis include erythrocyte sedimentation rate (ESR), C-reactive protein, complete blood count (CBC), liver function tests (LFTs), creatinine kinase, electrolytes (eg Na, K, Cl, Ca), glucose, thyroid function tests, and lactate dehydrogenase. Genetic testing may be considered upon diagnosis, particularly for the SOD1 and C9ORF72 genotypes.

Electrophysiological Studies  

The diagnosis of amyotrophic lateral sclerosis is supported by fasciculations in one or more regions, neurogenic changes in EMG results, normal motor and sensory nerve conduction, and absence of conduction block. If the diagnosis of amyotrophic lateral sclerosis is considered on clinical grounds, electrophysiological studies should be performed to confirm lower motor neuron dysfunction in clinically affected regions, to detect electrophysiological evidence of lower motor neuron dysfunction in clinically uninvolved regions, and to exclude other pathophysiological processes.  

Nerve Conduction Studies  

Nerve conduction studies may be used to exclude demyelinating motor neuropathies, which mimic amyotrophic lateral sclerosis. Motor nerve conduction is normal in the early stages of amyotrophic lateral sclerosis, but in advanced stages, denervation is observed, and this reduces muscle action potential amplitude.  

Electromyography (EMG)  

Findings in the EMG of amyotrophic lateral sclerosis patients include features of acute and chronic denervation and reinnervation. Not pathognomonic for amyotrophic lateral sclerosis, but similar abnormalities in several muscle proximal and distal limbs suggest a diagnosis of amyotrophic lateral sclerosis when there is no corresponding nerve root compression significant to cause the abnormality.

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Imaging

Neuroimaging Studies  

Neuroimaging studies are done to exclude other conditions. Advances in neuroimaging led to findings suggestive but not specific to amyotrophic lateral sclerosis: Corticospinal tract hyperintensity and cerebral atrophy detected in magnetic resonance imaging (MRI) and reduced primary motor cortex N-acetylaspartate to creatinine ratio in magnetic resonance spectroscopy.

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