Palatal myositis in horses with dorsal displacement of the soft palate.

The researchers investigated the muscles in the palates of 53 horses, many of which were racehorses, to understand how inflammation and muscle weakness contribute to the development of a common respiratory disorder called dorsal displacement of the soft palate. They found that these symptoms of inflammation, also known as myositis, were more prevalent in older horses and in those with the displacement condition.

Overview of Study and Findings

• The study aimed to understand the histologic and histochemical features of palatine muscles in horses and their connection to dorsal displacement of the soft palate, an upper respiratory issue prevalent among racehorses.
• Among the 53 horses studied, 25 were racehorses with past records of upper respiratory problems due to the dorsal displacement of the soft palate, while the remaining 28 were control horses with no respiratory issues.
• The researchers found noticeable pathologic features including myonecrosis, phagocytosis, mononuclear cell infiltration of perimysial connective tissue, alkaline phosphatase-positive myofibers, and myofibers with cytoarchitectural changes. These are signs indicative of myositis or inflammation of muscles.
• These signs of myositis were present in both groups of horses; however, their prevalence was noticeably higher in horses with the palate displacement condition.
• A higher prevalence of these inflammatory changes was observed in older horses regardless of whether they had the condition or were part of the control group.

Possible Causes of Myositis

• One of the inferences from the study was the possibility that weakness in the palatal muscle due to myositis might be contributing to the development of dorsal displacement of the soft palate.
• An alternate hypothesis suggested myositis might be a secondary effect as a result of trauma associated with displacement of the soft palate, although the study did not definitively confirm either hypothesis.
• The study also provided an observation that many horses dealing with dorsal displacement of the soft palate also had concurrent pharyngeal lymphoid hyperplasia.
• The researchers suggest that mucosal inflammatory changes related to this lymphoid hyperplasia may extend into the underlying palatine muscle, possibly explaining the higher prevalence of myositis.

The researchers conclude that further investigation is necessary to decipher whether palatal muscle myositis is a cause or result of soft palate displacement and to understand its relationship with pharyngeal lymphoid hyperplasia.