Endocrine Alopecia in Cats

In the past, feline symmetrical alopecia also has been called feline endocrine alopecia because it was thought to be due to a hormonal imbalance. However, the actual pathogenesis of this disease remains unknown.

No breed predilection has been reported. This condition is seen most frequently in neutered cats. Neutering at an early age has been hypothesized to play a role in the development of feline endocrine alopecia. Definite conclusions, however, cannot be drawn because great variation exists among affected cats in the time from neutering to the occurrence of hair loss.

In one study, many affected cats were thought to respond to thyroid hormone replacement like liothyronine. As a result of this study, decreased thyroid gland reserve was proposed as a cause of this condition.

As a group, affected cats had decreased response of their thyroid glands to thyroid-stimulating hormone (TSH), but some affected individuals had normal serum concentrations of the thyroid hormones, thyroxine (T4) and liothyronine (T3). Low thyroid gland reserve has been identified in humans after radioiodine therapy, surgical removal of the thyroid gland or cessation of prolonged thyroid hormone supplementation.

Feline endocrine alopecia has been hypothesized to result from a remnant of thyroid tissue that already has been maximally stimulated by the body's own thyroid-stimulating hormone (TSH) and cannot further respond to thyroid-stimulating hormone (TSH) administered as part of a diagnostic evaluation. It is important to note, however, that response to liothyronine (T3) therapy in affected cats does not necessarily imply the presence of thyroid gland disease because normal cats may temporarily grow hair back after thyroid supplementation. Furthermore, evaluation of serum liothyronine (T3) concentrations appears to be an unreliable indicator of thyroid function due to the location and function of T3 inside of cells.

Currently, feline endocrine alopecia is thought to have multiple causes and affected cats may respond to several different forms of hormonal replacement.

Clinical Presentation

Bilaterally symmetric alopecia or thinning of the hair coat, called hypotrichosis, is the main reason affected cats are presented to the veterinarian

The demarcation between affected and non-affected areas of the skin may or may not be well defined

Hair can be easily plucked from the skin

The skin usually is unaffected by the disease process. If skin lesions (crusts) are present, as in miliary dermatitis, other disease processes should be considered

Affected areas of the skin include the genital and perineal regions (19 percent of affected cats), the abdomen and inside portions of the hind legs (96 percent of affected cats), the back portions of the hind legs (50 percent of affected cats), the sides of the abdomen and the flanks (19 percent of affected cats), and the front limbs (42 percent of affected cats).