Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, affects approximately 30,000 individuals in the United States. This progressive and fatal illness results from degeneration of motor neurons in the brain, brainstem, and spinal cord. Skeletal muscle weakness such as that involving the extremities is observed first, but with time, bulbar, diaphragmatic and chest wall weakness cause respiratory compromise and eventual dependency upon mechanical ventilation. Although the exact prevalence of sleep apnea is not known in this population, respiratory insufficiency and failure are common. Most patients die from respiratory failure within five years from the onset of symptoms.
Respiratory insufficiency may occur during sleep despite normal daytime pulmonary function (53,54). One controlled study demonstrated a higher, though mild, AHI compared to controls. However, the subjects' sleep apnea predominated in REM sleep and consisted of periods of hypoventilation that accompanied significant oxygen desaturations (54). These nocturnal desaturations are related to hypoventilation rather than obstructive breathing (53). ALS patients with bulbar weakness or elderly with dyspnea are at higher risk for SRBD (55,56).
Respiratory symptoms and quality of life can be improved by intermittent mechanical ventilation (57). Orthopnea as well as daytime and nocturnal respiratory insufficiency improved after nocturnal nasal bilevel positive airway pressure (BPAP) therapy in one case (58). However, adherence to CPAP has been found to be poor in two other cases (59). Twenty-four-hour mechanical ventilation was associated with improved survival and quality of life especially in patients with orthopnea, daytime hypercapnea, and nocturnal desaturation (60). Polysomnographic investigation should focus on identifying features of hypoventilation and sleep apnea. ALS patients may frequently have difficulty turning, manipulating objects or even pushing a call button. Technologists should be aware of the patient's limitations and monitor the patient closely.
Clinicians should be aware that ALS patients have a progressive course and that their respiratory requirement will likely evolve as disease is worsened. Due to bulbar weakness, frequent leaks are encountered but may be reduced with the use of a full-face mask. Due to eventual upper extremity weakness, caregivers need to be involved in the placement of mechanical ventilation. Special attention to the effects of a sedative-hypnotic or pain medication is important to avoid further respiratory compromise.
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