The relationship between structural/MHC changes in upper airway palatopharyngeal muscle morphology and obstructive sleep apnea/hypopnea syndrome.

The aim of this study is to explore the relationship between structural/MHC changes in upper airway palatopharyngeal muscle morphology and obstructive sleep apnea/hypopnea syndrome. Palatopharyngeal muscle specimens were taken from 51 patients with obstructive sleep apnea hypopnea syndrome (OSAHS) who underwent uvulopalatopharyngoplasty (UPPP) resection. Patients were divided into light, medium and severe in terms of the severity of their OSAHS. There were 17 patients in each severity group. Palatopharyngeal muscle specimens were also taken from 17 patients suffering from chronic tonsillitis for comparison as the control group. All specimens were stained using Masson and observed for structural changes, especially in muscle fiber morphology, density and arrangement, as well as intermuscular connective tissues, under light microscopy. All specimens were also analyzed for MHC-I, MHC-IIa and MHC-IIb phenotype and protein expression differences using mRNA quantitative reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence staining. The results from each group were then statistically analyzed using semi-quantitative analysis. Light microscopy with Masson staining revealed that in the control group, the muscle fibers are closely connected and arranged neatly. In specimens from patients suffering from OSAHS, the palatopharyngeal muscle fibers are larger with obvious hypertrophy and there was an increase in elastic fibers. The mucosal lamina propria was thickened, and the density of muscle fibers was reduced. Muscle fibers are not neatly arranged and degeneration was observed. The amount of muscular pathology and fibrosis corresponds to the severity of disease in the patients. In patients with severe OSAHS, the proportion of collagen to muscle fibers was increased significantly. Immunofluorescence results reveal that there were significantly more fast muscle fibers and less slow muscle fibers in the study group than the control group. mRNA quantitative reverse transcription polymerase chain reaction (RT-PCR) revealed similar results, i.e., the proportion of MHC-II palatopharyngeal muscle fibers is higher in the study group than the control group, and increases with the severity of OSAHS. Pathological change occurs in both the collagen and muscle of OSAHS patients and corresponds to the degree of severity of OSAHS. Pathological change in palatopharyngeal muscle tissues is therefore, likely to be related to the occurrence and development of OSAHS. The increase in the proportion of the MHC-1I type fibers in OSAHS patients is likely to have an effect on the amount of airway support conferred by the muscle. This is likely the reason behind the lack of clinical improvement in some patients with severe OSAHS despite surgical treatment.