A better understanding of how Parkinson’s disease affects the laryngopharyngeal muscles of the esophagus could help identify those patients at risk for obstructive sleep apnea, according to a new study.
The research, “Laryngopharyngeal motor dysfunction and obstructive sleep apnea in Parkinson’s disease,” was published in the journal Sleep and Breathing.
Sleep impairment is a well-known non-motor symptom of Parkinson’s, but the relationship between this disorder and obstructive sleep apnea remains scarcely understood.
Although obstructive sleep apnea could be a comorbidity of Parkinson’s, as both are more prevalent in older populations, characteristics specific to Parkinson’s patients experiencing obstructive sleep apnea — such as an absence of obesity and a higher prevalence of upper airway obstruction and dysfunction — suggest other mechanisms are involved.
Proper functioning of laryngopharyngeal muscles is key to maintain upper airway opening and may be affected by Parkinson’s motor changes. Accumulation of the protein alpha-synuclein — the main component of Lewy bodies — in the vagus nerve (which extends from the head to the abdomen, and has sensory and motor functions) and in its pharyngeal branches could be an additional mechanism.
Laryngopharyngeal musculature motor dysfunction (LMD) may manifest by the presence of hypophonia – an abnormally weak voice due to a defect in vocal cord movement — that is common in Parkinson’s. Clinical evaluation of these muscles include tongue protrusion, elevation of the palate (or the roof of the mouth) and processes such as coughing, clearing one’s throat and swallowing, all of which require adequate muscle coordination.
A team of Brazilian researchers addressed whether changes affecting the laryngopharyngeal musculature and upper airway in Parkinson’s patients could be involved in the increased risk of obstructive sleep apnea.
A total of 48 Parkinson’s patients (41 men, mean age 66, and mean disease duration of 7.7 years) without chronic obstructive pulmonary disease, asthma requiring medication, or pneumonia were included in the study.
Participants underwent polysomnography, or a sleep study, to diagnose obstructive sleep apnea; how well their upper airway worked was evaluated by spirometry – a common test to assess breathing and respiratory disease; and researchers used a clinical protocol to analyze laryngopharyngeal muscles and a physical examination. “This study proposes a clinical evaluation of this musculature that can be performed at the bedside,” they wrote.
Thirty-one participants (64.6%) met the criteria for obstructive sleep apnea, with most (43.8%) having a mild form. The frequency of obstructive sleep apnea was higher here than in prior studies, which the scientists attributed to the predominance of men in their 60s and more sensitive obstructive sleep apnea diagnostic criteria.
Upper airway obstruction was found in 12 patients (25%) and LMD in 29 (60.4%). Having obstructive sleep apnea did not affect Parkinson’s characteristics, treatment dose, or pulmonary function. Clinical variables including obesity, snoring, neck circumference, and excessive daytime sleeping were also unchanged.
Hypophonia was the most common clinical indicator of LMD, detected in 58.3% of participants. Having laryngopharyngeal musculature motor dysfunction was linked to a more than threefold greater risk of obstructive sleep apnea.
Patients with LMD — compared to those without it — also had higher upper airway dysfunction (37.9 v. 10.5%), greater disease duration (8.7 v. 6.2 years), higher (worse) scores on the Unified Parkinson’s Disease Rating Scale Part III (UPDRSIII) of motor symptom severity (20 v. 15) and the Hoehn and Yahr scale of Parkinson’s symptoms (2.5 v. 2.0), as well as greater frequency of postural trunk and neck changes (51.7 v. 21.1%) and motor phenomena (65.5 v. 31.6%).
“The main finding of this study was a significant association between LMD and OSA [obstructive sleep apnea],” the researchers wrote. “These data support the hypothesis that dysfunction of this musculature can contribute to [obstructive sleep apnea in Parkinson’s].” More studies are needed to confirm the findings, however, they cautioned.
“LMD should be considered a factor that is involved in the obstructive phenomenon of UA [upper airway] in patients with OSA and [Parkinson],” the team concluded.