Evaluation of Body Weight, Body Condition, and Muscle Condition in Cats with Hyperthyroidism.
BACKGROUND
The contribution of fat loss versus muscle wasting to the loss of body weight seen in hyperthyroid cats is unknown.


OBJECTIVES
To investigate body weight, body condition score (BCS), and muscle condition score (MCS) in hyperthyroid cats.


ANIMALS
Four hundred sixty-two cats with untreated hyperthyroidism, 117 of which were reevaluated after treatment.


METHODS
Prospective cross-sectional and before-after studies. Untreated hyperthyroid cats had body composition evaluated (body weight, BCS, and MCS). A subset of these cats were reevaluated 3-12 months after treatment when euthyroid.


RESULTS
Pretreatment body weight (median, 4.36 kg; IQR, 3.5 to 5.2 kg) was lower than premorbid weight (5.45 kg; IQR, 4.6 to 6.4 kg, P < .0001) recorded 1-2 years before diagnosis. 154 (35.3%) cats were thin or emaciated; 357 (77.3%) had loss of muscle mass. Cats showed increases in body weight (median, 4.1 kg to 5.0 kg), BCS (median, 3/5 to 3.5/5), and MCS (2/3 to 3/3) after treatment (P < .001), but mild-to-moderate muscle wasting persisted in 45% of treated cats.


CONCLUSIONS AND CLINICAL IMPORTANCE
Most hyperthyroid cats lose body weight but maintain an ideal or overweight BCS, with only a third being underweight. As in human hyperthyroid patients, this weight loss is associated with muscle wasting, which affects >75% of hyperthyroid cats. Successful treatment leads to weight gain and increase of BCS in most cats, but almost half fail to regain normal muscle mass.
['Peterson|M E|ME|', 'Castellano|C A|CA|', 'Rishniw|M|M|']
D000818:Animals D001823:Body Composition D001835:Body Weight D002371:Cat Diseases D002415:Cats D065187:Controlled Before-After Studies D003430:Cross-Sectional Studies D005260:Female D006980:Hyperthyroidism D007457:Iodine Radioisotopes D008297:Male D009133:Muscular Atrophy D011446:Prospective Studies
Muscle condition Body composition Dietary protein Feline Sarcopenia Thyroid gland