Seasonal Flank Alopecia

By Tammy Hunter, DVM; Catherine Barnette, DVM

What is seasonal flank alopecia?

Seasonal flank alopecia is a skin condition in dogs that typically occurs during the winter months. Affected dogs lose patches of hair without any other significant evidence of skin disease. Seasonal flank alopecia typically begins in early adulthood and often continues on a yearly basis throughout the rest of the dog’s life.

Breeds commonly affected include boxers, Airedale terriers, English bulldogs, French bulldogs, and schnauzers. Seasonal flank alopecia is also seen in other breeds, although less commonly. (Image: Joel Mills. 2006. Wikipedia Commons. CC BY-SA 3.0.)

What causes seasonal flank alopecia?

The cause of this condition has not been determined, but it is thought to be caused by an abnormal response of the hair follicles to normal hormonal changes that occur with changing day length. This condition occurs primarily north of the 45-degree parallel.

This condition may have a genetic component in boxer dogs.

What are the signs of seasonal flank alopecia?

Affected dogs lose hair in well-demarcated areas, typically on the flanks (both sides of the abdomen, just in front of the rear legs). In most cases, this hair loss is symmetrical: each side of the body is equally affected. Hair loss can also occur in other areas, such as along the sides of the chest, at the tail base, or even across the bridge of the nose. When the hair falls out, the visible skin is often darker than usual (hyperpigmented).

"When the hair falls out, the visible skin is often darker than usual (hyperpigmented)."

Typically, hair loss begins in the fall and hair regrows in the spring. Less commonly, dogs may exhibit hair loss in the spring with regrowth in the fall. Regardless, the cycle of hair loss/regrowth typically follows a seasonal pattern, occurring repeatedly throughout the dog’s life.

How will my veterinarian diagnose seasonal flank alopecia?

In most cases, seasonal flank alopecia can be tentatively diagnosed on the basis of clinical signs. Well-demarcated regions of hair loss in a predisposed breed is highly suggestive of this condition.

Diagnosis of seasonal flank alopecia requires your veterinarian to rule out other possible causes for the hair loss. Bloodwork, including a complete blood cell count (CBC), serum biochemistry, and thyroid level, is often performed to rule out hormonal diseases that may cause similar patterns of hair loss. Skin scrapes are used to rule out mange and fungal cultures are used to rule out ringworm.

"A skin biopsy can be used to confirm the diagnosis of seasonal flank alopecia."

A skin biopsy can be used to confirm the diagnosis of seasonal flank alopecia. Your veterinarian will administer sedation or a local anesthetic, then remove a small sample of your pet’s skin. This skin sample is sent to a veterinary pathologist, who will process the sample and examine it under a microscope. The presence of characteristic hair follicle abnormalities can confirm the diagnosis of seasonal flank alopecia.

How is seasonal flank alopecia treated?

This condition is purely cosmetic, so no treatment is necessary.

If you choose to treat this condition for cosmetic reasons, melatonin is often used. Your veterinarian can help you determine an appropriate dose, after ruling out other possible causes of your dog’s hair loss. Melatonin typically leads to hair regrowth within 2–3 months. In dogs with a history of recurrent seasonal flank alopecia, melatonin may be started just before the typical time of onset and continued through the remainder of the season.

What is the prognosis for seasonal flank alopecia?

As a cosmetic condition only, the prognosis for seasonal flank alopecia is excellent. Even if it recurs year after year, it will have little or no impact on the health of the dog.

The progression of the condition from a cosmetic standpoint, however, is unpredictable. In some dogs, this condition occurs as an isolated incident, only once, and the hair regrows. In many cases, dogs with seasonal flank alopecia will be affected every year. In some dogs, the condition progresses over time. Rarely, the hair may fall out and never fully regrow.

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