Characterisation of phenotypic patterns in equine exercise-associated myopathies

Area of Science:

• Equine Medicine
• Veterinary Pathology
• Animal Myology

Background:

• Equine exercise-associated myopathies (EAMs) are common, diverse disorders causing muscle damage during exercise.
• Their causes are often unclear, hindering effective diagnosis and treatment.
• Lack of clear phenotypic characterization complicates genetic and disease research.

Purpose of the Study:

• To characterize distinct phenotypic patterns within equine exercise-associated myopathies.
• To identify potential subtypes based on clinical and histological features.

Main Methods:

• A historical cross-sectional study utilizing k-means clustering on clinical and histological data from 109 horses.
• Validation through principal components analysis, hierarchical clustering, and a blinded histological study of 69 horses.
• Comparison of phenotypic groups with controls and horses exhibiting myofibrillar disruption.

Main Results:

• Two broad phenotypes were identified: a non-classic exercise-associated myopathy syndrome (EAMS) subtype and a non-specific classic RER subtype.
• The EAMS subtype was significantly associated with clinical signs including muscle pain, reluctance to move, abnormal gait, ataxia, and paresis.
• No significant histological differences were found between subtypes in the validation study, and routine histopathology was not useful for sub-categorization.

Conclusions:

• Computational clustering reveals distinct phenotypic patterns in EAMs, supporting multiple disease subtypes.
• EAMS represents a novel subtype characterized by specific clinical presentations.
• Routine muscle histopathology is insufficient for categorizing these phenotypic subtypes.