The Pain and Sleep Relationship
Obstructive sleep apnea syndrome (OSAS) is a common yet underrecognized disorder. It is the most prevalent sleep disturbance observed at sleep disorder centers — of the approximately 75,000 patients seen annually in these centers, roughly 75 percent are diagnosed with OSAS.1,2 In the general population, OSAS affects approximately four percent of middle-aged adults and up to 50 percent of elderly persons.3,4 Projections of the prevalence of OSAS in the US range from seven to 18 million people.2
OSAS is a potentially life-threatening condition characterized by repeated collapse of the upper airway during sleep and cessation of breathing. The spectrum and severity of clinical presentations of OSAS are extremely variable.
In addition to its potential effect on mortality, OSAS can have a profound impact on quality of life. Many patients who suffer from OSAS experience pain, which further disturbs sleep. It is therefore important for caregivers who manage pain to be aware of the causes and treatment of OSAS.
Despite the prevalence of sleep apnea, the pathogenetic mechanisms of this disorder are not completely understood. Most of the data on the mechanisms of OSAS are derived from studies during non-rapid eye movement (NREM) sleep.
OSAS has been associated with anatomic compromise resulting from neoplasia (benign or malignant), metabolic abnormalities, and traumatic compromise. Inflammatory disorders may cause diffuse enlargement of structure such as the tongue and pharyngeal lymphoid tissues (as in tonsillitis), resulting in a compromise of the airway. However, in the majority of patients with OSAS, no specific focus of upper airway pathology can be identified.
Numerous mechanical factors may also influence upper airway closure and predispose a person to OSAS. These include upper airway caliber and compliance, load compensation, surface adhesive forces, pharyngeal luminal pressure, and thoracic caudal traction.
OSAS may occur in association with another primary sleep disorder called restless leg syndrome (RLS). RLS is characterized by intense pain or discomfort, mostly in the legs, during the evening when at rest. It is an akathisia and is often described as a “creepy sensation.” Patients with RLS note a strong urge to keep moving their legs or to get up and walk around to relieve the pain. RLS may significantly interfere with the onset of sleep.
Periodic limb movement disorder (PLMD) may accompany RLS or occur independently. This idiopathic condition is characterized by episodes of stereotypic rhythmic movement, usually of the legs, although other muscle groups (including the arms) may be involved. The patient’s bed partner typically perceives these episodes as kicks that occur in cycles of 20 to 40 seconds. Hundreds of limb movements may occur during a single night, but most of the time they do not awaken the affected person. They may, however, produce many brief arousals that disrupt sleep and decrease the amount of time spent in the deeper stages of sleep. The delayed sleep onset related to RLS and the sleep disruption from PLMD may cause daytime sleepiness.
RLS is primarily a clinical diagnosis. PLMD may be suspected based on information obtained from a bed partner. If necessary, the diagnosis can be confirmed by electromyography of limb-muscle activity during nighttime monitoring in a sleep laboratory.
There are no known causes of RLS. Caffeine and alcohol ingestion can aggravate and increase the frequency of RLS symptoms. Possible causes of RLS and PLMD include diabetes, Parkinson’s disease, rheumatoid arthritis, thyroid disease, iron and/or vitamin deficiency, and kidney dysfunction.
Like RLS, PLMD has no known causes. PLMD occurs only during sleep and involves unilateral or bilateral movements of limb muscles. The condition may be metabolic, vascular, or neurologic in origin. In addition to occurring commonly in patients with RLS, PLMD may occur in persons with OSAS.
Many persons with RLS and/or PLMD endure associated pain and other symptoms for years before seeking medical care, by which time they are in their 50s or 60s. Perhaps for this reason RLS and PLMD are associated primarily with geriatric patients; however, it is important to be aware that these primary sleep disorders can occur at any age.
Treatment should begin by examining the patient’s lifestyle and looking for opportunities to initiate lifestyle modification, particularly with regard to substances known to exacerbate symptoms (i.e., caffeine and alcohol). Because sleep loss can worsen symptoms, attention should be given to optimizing sleep habits.
For patients in whom changes in diet, drinking patterns, and sleep habits fail to reduce the symptoms of RLS and PLMD, drug therapy is indicated. Drug therapy is also indicated if there is pain associated with RLS or PLMD. There are four general classes of drugs used to treat RLS (and associated PLMD): dopaminergic agents, benzodiazepines, opioids, and anticonvulsants. Use of any agent should be viewed as a therapeutic trial; if symptom resolution does not occur within approximately one month, then a switch to another class of agents is a good idea.
Snoring and Sleep Apnea
Many people who snore or have OSAS mouth-breathe during sleep. Although this has not been systematically investigated, increased nasal or nasopharyngeal resistance might explain it.
Clinical studies have confirmed that nasal obstruction exacerbates a tendency toward OSAS.5 The larynx — the other high-resistance structure in the upper airway — can be the site of OSAS when compromised by space-occupying lesions or abductor paralysis.
Nonsurgical approaches to the management of OSAS include behavioral modification, drug therapy, continuous positive airway pressure (CPAP), and use of mechanical devices. Behavioral modifications include avoidance of alcohol and sedative medications, alteration of sleep position, avoidance of sleep deprivation, and weight loss. Drug therapy for OSAS is of limited clinical value, with the exception of thyroxine replacement in patients with hypothyroidism.14
Nonsurgical approaches to the management of OSAS include behavioral modification, drug therapy, continuous positive airway pressure (CPAP), and use of mechanical devices.
Continuous Positive Airway Pressure
Nasal CPAP is the initial treatment of choice for OSAS in adults and can reduce mortality and morbidity associated with OSAS.6 CPAP allows progressive restoration of air flow, as the pressure applied exceeds the airway opening pressure. CPAP works by pneumatically splinting the collapsible upper airway.