Definition & Overview

Neuromuscular disorders refer to a group of medical conditions characterized by the inability of the nerves and muscles to function normally. Patients with this type of disorder display a variety of symptoms, which may include sleep disturbance due to breathing problems.

The body’s muscles are either voluntary or involuntary. Voluntary muscles, such as those in the arms and legs, can be controlled according to a person’s wishes. Involuntary muscles, such as those found in the respiratory system, function without the person controlling them.

Neuromuscular disorders affect the strength of both voluntary and involuntary muscles; thus, the respiratory muscles have a tendency to be weak as well. The weakness of the respiratory muscles results in breathing problems, especially when sleeping.

Sleep usually occurs in 4 stages including the rapid eye movement (REM) stage. Stage 1 is when a person starts feeling drowsy while stage 2 is light sleep that progresses into a deeper sleep in stages 3 and 4. After stage 4, a person reaches the REM stage wherein dreaming occurs.

During sleep, a person has no control over both voluntary and involuntary muscles. In fact, the body temporarily paralyzes the voluntary muscles while the person is in deep sleep. The respiratory system muscles continue to function so a person can breathe and bring in oxygen. However, people with neuromuscular disorders have weak respiratory muscles, so their bodies are unable to receive the necessary amount of oxygen they require.

This results in reduced oxygen levels in the blood (hypoxemia) or increased blood levels of carbon dioxide (hypercapnia) that lead to fatal conditions, such as chronic respiratory failure.

Cause of Condition

There are quite a number of neuromuscular disorders. Those that affect the respiratory muscles and cause sleep disturbance include poliomyelitis, amyotrophic lateral sclerosis, post-polio syndrome, neuromuscular junctional disorders, myotonic dystrophy, myopathies, muscular dystrophies, and polyneuropathies.

All the above conditions cause weakness of one or more of the respiratory muscles, resulting in breathing difficulties during sleep, such as sleep hypoventilation. Hypoventilation is an abnormal slowness of breathing, resulting in low oxygen levels and increased carbon dioxide levels in the blood.

Hypoventilation can be a result of shallow breathing (hypopnea) or slow breathing (bradypnea). People with this condition often end up with sleep apnea (cessation of breathing).

Key Symptoms

The primary complaint of the majority of patients with a neuromuscular disorder that causes sleep disturbance is drowsiness during the day as a result of not sleeping well during the night. A good night’s sleep is not how many hours of sleep but the quality of sleep.

Good quality sleep begins with stage 1 sleep that progresses to stage 4 and then to REM. The sleep cycle takes about 120 minutes to complete, then goes back again to stage 2 and repeats for as many hours a person needs sleep.

People with a neuromuscular disorder usually have longer periods of stage 1 and 2. Some don’t even progress to REM. As a result, a person may be able to sleep the whole night, but not with the quality that the body needs to rejuvenate itself.

Many people with sleep disorders resulting from neuromuscular disorders are often undiagnosed and untreated while in the early stages, especially if they do not display any symptoms (asymptomatic). However, as the condition progresses, symptoms will begin to appear.

Who to See and Types of Treatment Available

Patients with sleeping problems should consult with their family doctors so the exact cause of the sleeping problem can be identified and treated to prevent the condition from worsening.

During the consultation, the doctor will inquire about the symptoms, which may include daytime fatigue, breathlessness, restlessness during sleep, and morning headaches. If the doctor suspects respiratory muscle weakness, several examinations will be performed to confirm the cause.

However, prior to the examinations, the doctor will first review the patient’s medical, psychiatric and sleep history, known diseases in the family, and even the patient’s present lifestyle. This information helps the doctor rule out other known causes of sleep disorders that are not associated with a neuromuscular disorder.

Of all the lab tests that will be performed, the most important will be the overnight polysomnographic recording test. This will be prescribed to patients with severe daytime drowsiness. Those who have a neurological disorder that will likely not influence the diagnosis and treatment of a sleep disorder won’t need to undergo the test. Other tests include a pulmonary function test to assess the function of the lungs.

The above-mentioned tests will allow the doctor to diagnose the exact cause of the condition, which is important in determining the most appropriate treatment method. The majority of sleep disorders are usually symptoms of an underlying medical condition. Treating the condition should help improve the ability to sleep as well as eliminate other symptoms of the condition by basically improving the patient’s ability to breathe. In the past, the most common form of treatment was an invasive procedure called tracheotomy. However, medical advances have allowed for non-invasive procedures, such as the use of positive or negative pressure ventilators.

Pressure ventilators help prevent hypoxemia or hypercapnia to improve the patient’s quality of life without necessarily treating the underlying cause of the condition. Nevertheless, primary treatment should always focus on the cause instead of the sleep disorder alone.

Other than medical treatment, a patient should also make necessary lifestyle changes, such as avoiding alcohol and caffeine beverages before going to bed, and redesigning the sleeping area to make it more conducive to sleep.

References:

  • Sateia MJ. International classification of sleep disorders-third edition: highlights and modifications. Chest. 2014;146:1387-1394. PMID 25367475 www.ncbi.nlm.nih.gov/pubmed/25367475.

  • Wakefield TL, Lam DJ, Ishman SL. Sleep apnea and sleep disorders. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head & Neck Surgery. 6th ed. Philadelphia, PA: Elsevier Mosby; 2015:chap 18.

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