Lower Motor Neuron Disorders

Disease

Distinctive Clinical and Pathological Features

Etiology

Anterior Horn Cells

Amyotrophic Lateral Sclerosis

Only disease with muscle wasting and increased reflexes

Specifically targets large motor neurons and corticospinal neurons

Appears to be due to a toxic gain in function of superoxide dismutase

Spinal Muscular Atrophy

Does not affect mental faculties (as opposed to DMD)

If children can survive childhood, they often live a normal lifespan

Due to degeneration of motor neurons in spinal cord

Assoc. w/defect of SMN1 gene on 5q

Plexuses

Brachial Neuritis

the sudden onset of severe pain, usually about the shoulder and often beginning at night, leading to a “flailed arm” in a week or two

no Tx; usually resolves spont.

Autoimmune process-- often preceded by an upper respiratory infection, hospitalization, vaccination, or non-specific trauma

Brachial plexus is also susceptible to infiltration by lung/breast CA; assoc. w/ tremendous pain

Involving the Peripheral Nerves

Hereditary aka Charcot Marie Tooth

It usually involves the legs before the arms

Can be mild and slowly progressive, so w/o patients w/high arch problems (“marked wasting of the more distal extremities, particularly the peroneal muscle groups, resulting in ‘stork legs.’”)

If a patient loses all peripheral sensory fibers, they often develop a mutilating neuropathy and present w/ cuts, burns, etc. on their hands.

PMP 22 gene duplication assoc. w/autosomal dominant type

Diabetic neuropathy

Effects mostly feet, hands

Pain predominates over weakness

Vasculitic neuropathy

Differential fasicular loss is the hallmark of vascular process affecting the peripheral nerves

Guillian Barre syndrome

Attacks peripheral myelin (as opposed to central in MS) but anywhere along its course, so patients can present w/ proximal or distal weakness

Classic presentation is profound weakness and early loss of reflexes

Can lead to severe weakness and even death

Inflammatory cells attack myelin; esp. post-Campylobacter infection antibodies attacking motor neurons

Most often a mixed neuropathy w/some sensory loss