Although naturally occurring hypothyroidism is very rare in cats, iatrogenic hypothyroidism is a recognized complication of treatment for hyperthyroidism. However, confirming the diagnosis of hypothyroidism in cats is not generally straightforward. The potential for false-negative and false-positive results exists with all thyroid function tests, especially in older cats that may have concurrent nonthyroidal illness. Therefore, all thyroid function test results must be interpreted in light of the cat's history, clinical signs, and other laboratory findings. If a low to low-normal serum thyroxine (T4) value is found in a cat that has been treated for hyperthyroidism, repeating the total T4 analysis, determining free T4 and thyroid stimulating hormone (TSH) concentrations, or performing a TSH stimulation test or thyroid scintigraphy may be needed to confirm the diagnosis.

In older cats presenting with clinical features of hyperthyroidism, confirming the diagnosis of thyroid disease is usually straightforward. However, the potential for false-negative and false-positive results exists with all thyroid function tests, especially when used for routine screening of large numbers of asymptomatic cats. Therefore, all thyroid function test results must be interpreted in light of the cat's history, clinical signs, and other laboratory findings. If a high serum thyroxine (T4) value is found in a cat that lacks clinical signs of hyperthyroidism, or if hyperthyroidism is suspected in a cat with normal total T4 concentrations, repeating the total T4 analysis, determining the free T4 concentration, or performing thyroid scintigraphy may be needed to confirm the diagnosis.

Heatstroke is a complex disease process that, in its most severe form, can result in multiorgan dysfunction and death. Heatstroke stems from the failure of the body’s thermoregulatory mechanisms, resulting in cellular damage and death. The organ systems most commonly affected in this disease process include the gastrointestinal tract and the coagulation, renal, cardiac, pulmonary, and central nervous systems. Heatstroke is diagnosed based on the patient history, physical examination, and clinicopathologic findings. Treatment should be instituted immediately to improve patient outcome and includes active cooling, fluid resuscitation, and supportive care. Patients with altered mental status, hypoglycemia, prolonged prothrombin time, and prolonged activated partial thromboplastin time at admission have increased mortality rates. Additional negative prognostic indicators include elevated serum creatinine level, delayed admission to the hospital, seizures, and obesity.

Feline inflammatory bowel disease is a diagnosis of exclusion and a common cause of chronic gastrointestinal signs suhc as weight loss, variation in appetite, vomiting, diarrhea, and lethargy. Patients with intestinal small cell lymphosarcoma can present identical clinical signs, and differentiating between these two conditions can be a challenge. A companion article discusses the value of performing immunohistochemistry and polymerase chain reaction testing on intestinal biopsy samples for this purpose.