Evaluation of muscle mass and intramuscular fatty infiltration in dogs with hypercortisolism and their association with prognosis

Abstract Background Muscle atrophy and intramuscular fatty infiltration, as well as their association with prognosis, have not been quantified in dogs with spontaneous hypercortisolism (HC). Objective To quantitatively evaluate muscle atrophy and IM fatty infiltration in dogs with HC and determine their prognostic impact. Animals Fifty‐three dogs with HC and 66 control dogs without HC. Methods Retrospective cohort study. Medical records and computed tomography images obtained between 2014 and 2021 were evaluated. Kaplan‐Meier curves and log‐rank tests were used to analyze the effect of muscle atrophy and IM fatty infiltration on the prognosis of dogs with HC. Results Dogs with HC showed lower visually measured cross‐sectional area (VCSA) and cross‐sectional area based on attenuation (HCSA) than control dogs (median [interquartile range {IQR}]: 50.3 mm2/mm [36.2‐67.8] vs 66.7 mm2/mm [48.0‐85.9]; P < .001; 30.4 mm2/mm [13.7‐57.2] vs 54.8 mm2/mm [39.7‐71.5]; P < .001, respectively). Dogs with HC had lower epaxial muscle attenuation (L3HU) than control dogs (median [IQR]: 21.2 Hounsfield [HU] [12.4‐28.2] vs 33.2 HU [22.6‐43.6]; P < .001). Dogs with HC with lower HCSA or L3HU had shorter survival (median [IQR]: 670 days [222‐673] vs 949 days [788‐1074], P < .01; 523 days [132‐670] vs 949 days [756‐1074], P < .01, respectively) but not lower VCSA (median [IQR]: 673 days [132‐788] vs 949 days [523 to not applicable]; P = .30). Conclusion and Clinical Importance Hypercortisolism in dogs causes muscle atrophy and IM fatty infiltration and is associated with poor prognosis