Endocrine Alopecia in Cats

Overview of Feline Endocrine Alopecia

Feline endocrine alopecia is a rare skin condition of cats. The cause is unknown but it is hypothesized to be hormonal in origin. Several hormones have been considered to play a role in feline endocrine alopecia including thyroid hormone, estrogen and testosterone.

Below is an overview of Endocrine Alopecia in Cats followed by in-depth information about the diagnosis and treatment options for this problem.

Affected cats experience thinning of the hair or hair loss, which has a similar distribution on both sides of the body including the flanks, abdomen and hind legs. Cats may spend considerable time grooming themselves without being observed by their owners. In many instances, hair loss is self-inflicted rather than spontaneous. An important first step in affected cats is to determine whether or not the hair loss is self-inflicted.

One approach is to use a plastic cone collar (an Elizabethan collar) to prevent the cat from grooming and observe whether or not the hair grows back. If the hair grows back, the next step is to determine why the cat is grooming excessively. In most instances, excessive self-grooming is a sign of allergy rather than being psychological in origin.

If the hair does not grow back, self-grooming is not the cause and your veterinarian will proceed with a diagnostic evaluation to determine the cause of the hair loss.

Feline endocrine alopecia primarily is a cosmetic problem. An important initial step is to rule out medical conditions that may mimic this condition and would require medical therapy.

Conditions that may mimic feline endocrine alopecia and require medical therapy include allergies of various types, dermatophytosis (ringworm) and parasitic diseases.

Veterinary Care

• Microscopic observation. The first step in the evaluation of the cat with feline endocrine alopecia is to pluck several hairs for observation under the microscope to determine whether or not they are broken. The occurrence of short, broken hairs suggests that the cat is grooming excessively. The presence of relatively normal-appearing hairs under the microscope suggests spontaneous hair loss.
• Skin scrapings. These help to rule out certain parasitic diseases such as mange mite infestation.
• Fungal culture. A sample of hair also can be sent to a laboratory for fungal culture to determine whether or not the cat has ringworm (dermatophytosis). Ringworm infestation could cause the hair to fall out spontaneously.
• Blood samples. These may be submitted to the laboratory for measurement of specific hormones to evaluate endocrine function.

If other diseases are ruled out, a diagnosis of feline endocrine alopecia is made. Fortunately, this condition is primarily a cosmetic condition and does not jeopardize the health of the animal.

Cats with feline endocrine alopecia are otherwise healthy. Treatments used in an attempt to stimulate regrowth of hair have the potential to cause adverse effects, some of which are potentially serious. Also, because the cause of feline endocrine alopecia is unknown, several treatments may be tried before a response is observed.

Home Care

• You may be asked to place a plastic cone collar (Elizabethan collar) on your cat to determine whether or not excessive self-grooming is the cause of your pet’s hair loss.
• You may be asked to follow an elimination diet trial with a new source of protein to rule out the possibility of food allergy.
• Aggressive flea control will be recommended, especially in geographical areas with a temperate climate.
• If you decide to pursue medical treatment for your cat with endocrine alopecia, you may be asked to administer medications orally once or twice per day or you may be asked to bring your cat to the clinic for injections. Usually, a few injections are necessary.
• Some of the medications used to treat feline endocrine alopecia can cause cardiac complications whereas others may cause liver toxicity, mammary gland tumors, diabetes mellitus, or behavioral changes.
• It is important that you take your cat back to your veterinarian for regular check ups to monitor blood counts and serum chemistry during treatment.

In-depth Information on Feline Endocrine Alopecia

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).

Diagnosis In-depth

It is important to determine whether the alopecia is self-inflicted or spontaneous. Cats may spend considerable time grooming themselves while unobserved by their owners, and frequently it is not obvious whether the hair loss has been self-inflicted or spontaneous.

• Self-inflicted hair loss is more common than feline endocrine alopecia and should be considered first.
• Examination of the tip of the hair under the microscope helps differentiate spontaneous hair loss from a self-inflicted hair loss. In many cats with symmetric alopecia, the hair tips are broken suggesting excessive self-grooming and an underlying pruritic or itchy disease.
• Alternatively, a plastic cone (Elizabethan collar) may be used for a few weeks to monitor hair growth. If hair regrowth occurs, self-inflicted hair loss due to an underlying pruritic skin disease should be considered.
• Pruritic skin diseases in cats include flea allergy, atopy, food allergy, dermatophytosis (ringworm) and mange mite infestation.
• Medical history including age of onset, seasonality, response to treatment with cortisone-like drugs such as glucocorticoids and clinical signs will help your veterinarian rank these different possible diseases.
• All cats with symmetric alopecia should have several skin scrapings performed and hairs from affected skin should be submitted for fungal culture to identify dermatophytosis (ringworm).
• An aggressive flea control program should be instituted. A dietary change may be appropriate in cats that do not have seasonal disease.
• Non-pruritic skin diseases in cats include dermatophytosis (ringworm), demodectic mange, telogen effluvium (loss of hairs in resting phase from their follicles), overactivity of the adrenal glands (hyperadrenocorticism) and hypothyroidism (which is extremely rare in cats).
• A diagnosis of feline symmetric alopecia is made by exclusion of other diseases.
• A complete blood count and serum chemistry tests are normal in cats with symmetric alopecia.
• Skin biopsies from affected cats show telogen hairs (hairs that are in a resting phase rather than in a growing phase).
• These findings, however, are not specific for this condition, and most of the hairs in normal cats may be in the resting (i.e. telogen) phase.

Treatment In-depth

• Feline symmetric alopecia primarily is a cosmetic condition, and not treating it does not harm the general health of the cat.
• Treatments that have been attempted in cats with symmetric alopecia have the potential to cause adverse effects. You should ask your veterinarian about the potential risks of possible medical treatments.
• Liothyronine (a thyroid hormone also called T3) can be administered at an initial dosage of 20 micrograms per cat twice per day. The dosage is gradually increased to 50 micrograms twice per day.
• The gradual increase in dosage is recommended to minimize possible adverse effects that may arise from an increase in cellular metabolism caused by liothyronine (T3) administration.
• The main adverse effect of excessive liothyronine (T3) is cardiac arrhythmias, which resolve with discontinuation of the drug.
• Hair regrowth may occur in 4 to 10 weeks.
• A positive response to liothyronine (T3) therapy does not necessarily imply the presence of thyroid gland disease, because thyroid hormones have the ability to stimulate hair growth in normal individuals.
• Alternatively, a combination of androgens and estrogens may be tried. Testosterone may be used at 12.5 milligrams and diethylstilbesterol at 0.625 milligrams administered intramuscularly.
• Adverse effects that may be seen with androgen and estrogen therapy include liver toxicity, personality change, bone marrow suppression, and aggression.
• Injections may be repeated in 6 weeks if no response is seen after the first injection.
• Hair regrowth should begin within 2 to 4 weeks and a complete response should be observed within 2 to 3 months.
• Relapses are not uncommon and may occur within 6 months or up to 2 years after discontinuation of therapy.
• Additional therapy usually is successful.
• Progesterone-like drugs (e.g. megestrol acetate, medroxyprogesterone acetate) are not licensed for this use in the United States and are not recommended due to the possibility of severe adverse effects.
• These adverse effects include diabetes mellitus, adrenal gland suppression, and mammary gland hyperplasia or neoplasia (i.e. cancer).

Follow-up

Some cases of feline symmetric alopecia are idiopathic (of unknown cause) whereas others are allergy-related. The only known underlying disease that can be prevented is flea allergy. Thus, aggressive flea control measures are strongly recommended.