Motor neuron diseases (mnds) are a heterogeneous group of neurologic conditions characterized by corticospinal tract and anterior horn cell degeneration of the brain and spinal cord1 (Fig. 71–1). While the etiology of MNDs is broad and not clearly elucidated, there is evidence supporting multifactorial processes that can be inherited genetically or acquired sporadically through environmental exposures such as toxins, infections, and autoimmune or other causes.2–8 The common pathology is the destruction of motor neurons and encompasses disorders with selective loss of lower motor neurons (LMNs), upper motor neurons (UMNs), or a combination of both.2 This results in muscle weakness and disability with loss of normal limb, speech, swallow, and respiratory functions.
(Left panel) Cervical spinal cord in amyotrophic lateral sclerosis shows dramatic atrophy of gray matter in anterior horns (arrow) due to loss of motor neurons. The pale-staining areas in the lateral and anterior columns (arrowheads) of the spinal cord reflect the great loss of myelinated axons in the lateral and anterior corticospinal tracts. (Right panel) Normal cervical spinal cord. (Photo contributor: Kinuko Suzuki, MD, Tokyo Metropolitan Institute of Gerontology; retired faculty, Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC.)
The most common adult form of MND is amyotrophic lateral sclerosis (ALS), which is characterized by both UMN and LMN findings1 (Fig. 71–2). ALS, first described by Jean-Martin Charcot in the 1870s, is considered to be the classic model of MND.1 In the United States, for three-quarters of a century, ALS was referred to as “Lou Gehrig's disease,” named after a beloved American baseball player who publicly announced the end of his career due to the disability caused by the disease. This moniker, however, has fallen out of favor since a very successful research fund-raising campaign (known as the “ALS Ice Bucket Challenge”) caused a shift in the public's recognition of the disease. In this chapter, we discuss MND classification, diagnostic and clinical evaluation, and treatment and management strategies from the perspective of reaching a diagnosis and treating the patient found to have ALS.
Ventral view of the spinal cord (with the dura opened) of a patient with motor neuron disease (amyotrophic lateral sclerosis). Notice the reduction in size of the ventral roots (resulting from the degeneration of the axons of motor neurons) compared with the normal dorsal roots. (Reproduced with permission from Discussion of Cases. In: Waxman SG, eds. Clinical Neuroanatomy, 28e New York, NY: McGraw-Hill; 2017.)
CLASSIFICATION OF MOTOR NEURON DISEASE (SEE TABLE 71–1)
MNDs are initially classified by the presence of UMN, LMN, or combined UMN and LMN signs and symptoms.3 Using this taxonomy allows the clinician to ...