Pathophysiology
The variety of medical disorders capable of presenting with weight loss as the chief complaint is vast and the ability to obtain a diagnosis can seem daunting. Fundamentally, weight loss occurs when the metabolic demand for energy or the loss of nutrients exceeds energy intake.
By keeping this principle in mind, one can systematically and methodically rule out potential causes and achieve the correct diagnosis in most cases.Inadequate energy intake may occur as a result of feeding an inferior diet containing nutrients of low bioavailability. Alternatively, the patient may not be ingesting a sufficient amount of calories to meet their maintenance energy requirements (MER).1
■ Dogs: MER (metabolizable kcal/day) = 2 [70(wtkg0,75)].
■ Cats: MER (metabolizable kcal/day) = 1.4 [70(wtkg0,75)].
Another cause for weight loss is nutrient malassimilation that can be caused by anorexia, regurgitation, dysphagia, vomiting, maldigestion, or malabsorption. All of these conditions may prevent sufficient caloric intake to meet the patient’s energy requirements.
Increased loss of nutrients occurs with disorders such as PLE, PLN, gastrointestinal bleeding, glucosuria (e. g., diabetes mel- litus), or in burn victims experiencing extensive loss of protein-rich exudate from skin injuries.
Finally, weight loss may be caused by increased energy utilization due to hypermetabolic states, such as feline hyperthyroidism or due to neoplastic diseases.
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