neurologic disorders
Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs)
Symptoms and Signs of ALS and Other MNDs
Upper MNDs(eg, primary lateral sclerosis) affect neurons of the motor cortex, which extend to the brain stem (corticobulbar tracts) or spinal cord (corticospinal tracts). Generally, symptoms consist of stiffness, clumsiness, and awkward movements, usually affecting first the mouth, throat, or both, then spreading to the limbs. affect the anterior horn cells or cranial nerve motor nuclei or their efferent axons to the skeletal muscles. In bulbar palsies, only the cranial nerve motor nuclei in the brain stem (bulbar nuclei) are affected. Patients usually present with facial weakness, dysphagia, and dysarthria. When anterior horn cells of spinal (not cranial) nerves are affected, as in Spinal Muscular Atrophies (SMAs) , symptoms usually include muscle weakness and atrophy, fasciculations (visible muscle twitches), and muscle cramps, initially in a hand, a foot, or the tongue. Physical findings help differentiate upper from lower MNDs (see table Distinguishing Upper From Lower Motor Neuron Lesions ) and weakness due to lower MNDs from that due to myopathy (see table Most patients with ALS present with random, asymmetric symptoms, consisting of cramps, weakness, and muscle atrophy of the hands (most commonly) or feet. Weakness progresses to the forearms, shoulders, and lower limbs. Fasciculations, spasticity, hyperactive deep tendon reflexes, extensor plantar reflexes, clumsiness, stiffness of movement, weight loss, fatigue, and difficulty controlling facial expression and tongue movements soon follow. Other symptoms include hoarseness, dysphagia, and slurred and often nasal speech; because swallowing is difficult, salivation appears to increase, and patients tend to choke on liquids. Late in the disorder, a pseudobulbar affect occurs, with inappropriate, involuntary, and uncontrollable excesses of laughter or crying. Sensory systems, consciousness, cognition, voluntary eye movements, sexual function, and urinary and anal sphincters are usually spared. Death is usually caused by failure of the respiratory muscles; 50% of patients die within 3 years of onset, 20% live 5 years, and 10% live 10 years. Survival for > 30 years is rare. The bulbar muscles innervated by cranial nerves are predominantly affected, resulting from progressive degeneration of the motor neurons innervating bulbar musculature. This disorder causes progressive difficulty with chewing, swallowing, and talking; a nasal voice; reduced gag reflex; fasciculations and weak movement of the facial muscles and tongue; and weak palatal movement. Aspiration is a risk. The upper motor neuron equivalent of this disorder is progressive pseudobulbar palsy. This disorder affects the corticobulbar tract, descending to bulbar lower motor neurons, but spares the lower motor neurons in the brain stem, causing upper motor neuron weakness of the bulbar muscles. and thus is called pseudobulbar. Speech is spastic, patients cannot rapidly repeat syllables, (kakaka, tatata, lalala, bababa); gag reflex and jaw jerk are brisk. A pseudobulbar affect with emotional lability may also occur. Commonly, progressive bulbar palsy spreads, affecting extrabulbar segments; then it is called bulbar-variant ALS. Patients with dysphagia have a very poor prognosis; respiratory complications due to aspiration frequently result in death within 1 to 3 years. In many cases, especially those with childhood onset, inheritance is autosomal recessive. Other cases are sporadic. The disorder can develop at any age. Anterior horn cell involvement occurs alone or is more prominent than corticospinal involvement, and progression tends to be more benign than that of other MNDs. Fasciculations may be the earliest manifestation. Muscle wasting and marked weakness begin in the hands and progress to the arms, shoulders, and legs, eventually becoming generalized. Deep tendon reflexes are hypoactive. Patients may survive≥25 years. Suspect ALS or another motor neuron disease in patients who have features of upper and/or lower motor neuron dysfunction (eg, extensor plantar responses plus atrophy and fasciculations). In primary lateral sclerosis, progressive muscle stiffness in the arms and legs occurs with spasticity and hyperreflexia during examination. Fasciculations and muscle atrophy are atypical for this predominantly upper motor neuron disorder. Survival is prolonged because risk of aspiration and pneumonia is low; several years must pass to result in total disability. 