Diagnostic criteria for equine thoracolumbar myofascial pain syndrome: A foundational study

Diagnostic criteria for myofascial pain syndrome (MPS) are well established in humans but remain underexplored in horses. This study aimed to identify which MPS clinical signs were present in the equine thoracolumbar region, assess internal coherence among clinical indicators, and explore the diagnostic relevance of owner-reported behavioural, signalment, management, and clinical variables. A population of 120 horses underwent a static physical assessment of the thoracolumbar region. Owner-reported horse behaviours were collected through a questionnaire. Taut band, hypersensitive spot, local twitch response (LTR), jump sign, restricted range of motion (ROM), pain score (0-5), and global ROM score (0-4) were assessed by manual palpation. Machine-learning (ML) regression models were used to examine multivariate predictive patterns. A taut band and a hypersensitive spot were present in all horses, whereas an LTR was absent. The jump sign was identified in 71.7% and restricted ROM in 69.2% of horses. The median pain score was 4 (IQR 3-4, range 2-5). Jump sign correlated with pain score (ρ = 0.814, p < 0.001), and restricted ROM correlated with global ROM score (ρ = 0.749, p < 0.001). Owner-reported behaviours had a weak relationship with pain on palpation (ρ = 0.218, p = 0.017). Stabled horses had higher pain scores (p = 0.044) and greater ROM restriction (p = 0.013) than horses kept outdoors. Machine learning identified the jump sign as the dominant pain predictor (>90% importance) and a robust clinical marker. Taut band, hypersensitive spot, and jump sign emerged as key clinical findings associated with equine thoracolumbar MPS, providing novel insights into the clinical variables characterising this condition in horses.