Evaluation of the diagnostic accuracy of skeletal scintigraphy in lame and poorly performing sports horses

Abstract

Skeletal scintigraphy is an established imaging modality, however, its validity as a diagnostic test in lame or poorly performing sports horses has not been determined. The objective of this retrospective cross-sectional analytical study was to determine the accuracy of skeletal scintigraphy as an indiscriminate screening test in sports horses. All sports horses that underwent scintigraphic examination between March 2008 and December 2014 for which a definitive diagnosis was reached were included. Examinations were evaluated blindly. Characteristics of increased radiopharmaceutical uptake were recorded and subjectively categorized as possibly relevant or non-relevant. Kappa statistics were used to assess agreement between test results and final diagnosis. There were 1222 positive clinical diagnoses in 480 horses, of which 687 regions (56.4%) had no associated increased radiopharmaceutical uptake and 99 regions (8.1%) had non-relevant increased radiopharmaceutical uptake. The sensitivity of increased radiopharmaceutical uptake for identification of final diagnosis was low (43.8%) and specificity was high (94.0%). The agreement was fair (κ = 0.36). Relevance categorization improved the test; the sensitivity for final diagnosis was low (35.7%), specificity was high (98.9%), and the agreement was moderate (κ = 0.45). The agreements of increased radiopharmaceutical uptake and relevance categorization with final diagnosis were only substantial for feet (κ = 0.67 and κ = 0.66, respectively) and proximal aspect of the forelimb (elbow, shoulder, and scapula combined) (κ = 0.69 and 0.78, respectively). Scintigraphic examination is unlikely to lead to a full and correct diagnosis of the cause(s) of lameness or poor performance in sports horses when used as an isolated or indiscriminate screening tool.

Evaluation of the diagnostic accuracy of skeletal scintigraphy for the causes of front foot pain determined by magnetic resonance imaging

“…Based upon the characteristics of increased radiopharmaceutical uptake and existing scientific knowledge, each area of increased radiopharmaceutical uptake was subjectively categorized as being either likely or unlikely to be of clinical relevance. Good inter‐ and intra‐interpreter agreement for this grading and relevance categorization system has been previously reported …”

“…The horses included were part of a larger population of horses that underwent skeletal scintigraphy in which overall there was good agreement between increased radiopharmaceutical uptake anywhere in the foot and a final diagnosis of foot pain . The age and gender distribution was very similar between the two study populations.…”

“…To be included in the study, all horses must have undergone clinical and lameness evaluations by veterinary surgeons specializing in equine orthopedics (Royal College of Veterinary Surgeons Specialists in Equine Orthopaedics), diagnostic analgesia which localized pain contributing to lameness or poor performance in one or both front feet, skeletal scintigraphy of both front feet (including dorsal, lateral, and solear images) and MRI must have resulted in a definitive diagnosis. The horses included formed part of a previous study population …”

“…Radiopharmaceutical uptake has been described in association with abnormalities of the navicular bone, collateral ligaments of the distal interphalangeal joint, deep digital flexor tendon, distal phalanx, and ungular cartilages . There was substantial agreement between increased radiopharmaceutical uptake anywhere within the foot and a final diagnosis of foot pain, with moderate sensitivity and high specificity . Subjective relevance categorization based upon the characteristics of increased radiopharmaceutical uptake slightly decreased the sensitivity, but increased the specificity.…”

“…Despite the widespread use of skeletal scintigraphy, a recent study demonstrated that it does not meet the minimum diagnostic reliability to be used as an indiscriminate screening tool for sports or leisure horses with lameness or poor performance . The agreement between both the presence of increased radiopharmaceutical uptake and subjective interpretation of increased radiopharmaceutical uptake with final diagnosis was variable among anatomical regions.…”