Reasons for performing study: To present the first report of a case series concerning equine idiopathic muscular hypertrophy of the oesophagus (IMHO).
Objectives: To investigate the clinical and pathological features of the disorder.
Methods: The medical records of 31 horses suffering from the disorder were reviewed retrospectively. In all these animals the diagnosis was confirmed at post mortem examination.
Results: The median age of the affected horses was 12.5 ± 5.6 years (range 1–26) without sex or breed predilection. Only 2 out of 31 horses showed clinical signs associated with oesophageal dysfunction, indicating that the muscular hypertrophy was rather a coincidental post mortem finding. Histology revealed thickening of the distal portion of the oesophagus mainly involving the circular layer of the tunica muscularis without fibrosis or inflammation. In 8 cases, the disorder was seen in concurrence with idiopathic hypertrophy of the tunica muscularis of various other parts of the gastrointestinal tract.
Conclusions: In the majority of patients, IMHO was a coincidental finding at post mortem examination usually confined to the smooth, circular muscle layer of the tunica muscularis externa.
Potential relevance: Further research is necessary to study the precise effect of IMHO on oesophageal function.