Alopecia X and seasonal flank alopecia in dogs

Overview

Alopecia means hair loss, while hypotrichosis means thinning of the coat. Alopecia X is also called black skin disease, or BSD, because exposed skin may darken.

The X refers to the fact that its exact mechanism remains unknown. In seasonal flank alopecia, hair disappears from clearly defined areas of the flanks, and the disorder is usually cosmetic.

Despite the name, flank alopecia does not recur regularly in the same season in every dog. Alopecia X does not spread to other dogs.

Alopecia X is not expected to shorten a dog's life.

Causes

The hair growth cycle stops

A follicle normally goes through a growth phase, a brief regression phase and a resting phase, after which the old hair is shed. Alopecia X involves few follicles in the growth phase, with resting and empty follicles predominating.

With a disrupted cycle, old hair is shed normally but new hair does not replace it normally. A follicle may remain empty after shedding before another growth phase begins.

Abnormal sex hormone metabolism or follicular hormone responses have been suspected, but no link has been confirmed. A small molecular study compared skin from five affected Pomeranians with four healthy dogs of the same breed.

In affected skin, activity of genes in the growth-associated Wnt and Shh signalling pathways was reduced.

Day length and flank alopecia

The exact cause of flank alopecia remains unclear, but an association with day length and climatic variation is recognised. The pineal gland secretes most melatonin during winter, when daylight hours are short.

An abnormal follicular response to normal hormonal signals changing with day length has been suggested, but the precise mechanism has not been confirmed.

Risk factors

Alopecia X often starts in a young adult, particularly in densely coated Spitz breeds. It is especially recognised in Pomeranians, but also occurs in Keeshonds, Samoyeds and Chow Chows, among others.

Both males and females can be affected, whether neutered or not. In Pomeranians, alopecia X is more common in males.

Flank alopecia most often begins at 3–6 years, but occurs across about 1–11 years of age. Predisposed breeds include Boxers, Airedale Terriers, English Bulldogs, French Bulldogs and Schnauzers.

The seasonal form is mainly diagnosed north of latitude 45°N.

Typical symptoms

In alopecia X, loss of guard hairs may be the first change before more extensive baldness.

• The remaining coat becomes dry, dull or soft and fluffy.

• Hair thins on the flanks and areas exposed to friction.

• Alopecia X may extend to the neck, trunk, tail and thighs.

• Hair on the head and lower limbs is generally preserved.

• Bald skin may become much darker than surrounding skin.

• Flank alopecia usually produces sharply defined bald patches on both sides of the body.

• Flank alopecia may also affect only one side.

• Regrowing hair may be a different colour from before.

Flank alopecia may also cause bald areas on the sides of the chest, tail base or top of the muzzle. The most common seasonal pattern is hair loss in autumn and regrowth in spring, but some dogs show the reverse pattern.

Alopecia X does not usually cause pain or itching. Skin and coat around seasonal flank alopecia generally look normal.

Complications and consequences

Distinguishing skin changes from systemic disease

A dog with alopecia X is usually otherwise healthy despite a marked change in appearance. Flank alopecia also generally leaves overall health unaffected, even when it recurs each year.

In some dogs with flank alopecia, hair no longer grows back completely. After alopecia X, spontaneous regrowth without treatment is uncommon.

Some dogs have only one episode of flank alopecia in their lifetime, followed by full coat recovery. A coat restored by treatment may thin again later.

Itching may develop if a secondary bacterial infection accompanies otherwise non-inflammatory hair loss.

Diagnosis at the vet

History and skin examination

The vet asks about age at onset, the first areas affected and seasonality. An unspayed female's cycle is reviewed, because phantom-pregnancy-related shedding may start 4–6 weeks after a season, particularly around the collar and rear body.

As phantom pregnancy settles, this separate hair loss generally resolves on its own without being alopecia X. Medication and exposure to hormonal products are part of the history, because they can also cause hair loss.

Increased drinking, urination and eating may direct investigations towards Cushing's disease. Weight gain and tiredness may instead raise suspicion of hypothyroidism.

Severe illness, a stressful event or pregnancy 1–4 months before shedding may suggest separate telogen effluvium. In this condition, many follicles enter the same cycle phase together, potentially causing sudden, widespread hair loss.

Thin, inelastic abdominal skin and blackheads are findings consistent with Cushing's disease. Enlarged nipples and abnormal testicles in an uncastrated male may prompt investigation of excess oestrogen effects.

The vet assesses whether hair loss is localised or widespread and whether inflammation is present. Skin scrapings look for hair-loss-causing mites, such as Demodex.

A cell sample can identify secondary bacterial or yeast infection. Fungal culture can investigate whether ringworm is responsible.

Microscopic hair examination, called a trichogram, may show broken tips revealing licking or other self-inflicted damage. Abnormal pigment clumps in the shaft may instead suggest a follicular structural disorder associated with colour dilution.

Root shape helps distinguish growing from resting hairs. If bacterial infection inflames the skin, it is treated first, then the original pattern of hair loss is reassessed.

Blood tests and skin biopsy

A blood count, biochemistry and urine sample assess general health and organ function. Thyroid and adrenal tests are chosen according to symptoms to rule out hormonal alternatives.

In a skin biopsy, the pathologist assesses follicles and looks for other inflammatory or structural skin conditions. A skin biopsy alone cannot confirm alopecia X.

Typical tissue changes in flank alopecia support the diagnosis alongside the clinical picture. An abnormal broad sex hormone panel may also occur in a healthy dog, complicating interpretation.

Hair growth after thyroid hormone administration does not prove that a dog had hypothyroidism.

Treatment

Monitoring is often sufficient

The vet prescribes treatment and any medication only after diagnosis and assessment of the dog's other health conditions. Cosmetic flank alopecia does not have to be medicated if the dog is otherwise healthy.

Hair in seasonal flank alopecia may return spontaneously in spring or summer. Alopecia X can also be monitored without stronger treatments if simpler options do not help.

Treatments affecting reproduction and melatonin

Spaying or castrating an intact dog with alopecia X may trigger regrowth. However, baldness may return years after such a response.

Melatonin may promote coat recovery in about 40–60% of dogs with alopecia X. It can cause drowsiness.

Diabetes is a contraindication to its use. Inactive ingredients also matter: xylitol in some melatonin products is toxic to dogs.

Regrowth may be seen within 2–3 months during melatonin treatment for flank alopecia. Its contribution is difficult to assess because spontaneous regrowth is so common.

A deslorelin implant that reduces sex hormone production may help some uncastrated males with alopecia X. Evidence for use in neutered dogs is limited.

Deslorelin is generally avoided in unspayed females, so treatment considered for a male does not automatically apply to a female.

Microneedling and risks of stronger medicines

Microneedling creates controlled small punctures in the skin to stimulate hair growth. It can be painful and requires appropriate anaesthesia and pain relief.

Medicines inhibiting cortisol production can have serious adverse effects and require repeated adrenal function monitoring. Excessive reduction of adrenal hormones is a possible complication.

Growth hormone treatment may carry a risk of temporary or permanent diabetes.

Prevention

The inheritance pattern of alopecia X is unknown, although breed predisposition and family histories suggest an inherited basis. Some Spitz breed clubs recommend not breeding from an affected dog.

A breeding diagnosis cannot be made from bald appearance alone, because conditions such as hypothyroidism and fungal infection must first be ruled out. The association between flank alopecia and seasons does not mean that increasing light exposure alone is a proven preventive measure.

Tracking symptoms helps identify a recurring seasonal pattern, because flank alopecia often returns at roughly the same time of year.

Important for dog owners

Photograph the flanks and other changing areas in similar light. Note when the coat began thinning and when new hair appeared. Also record treatments tried and possible adverse effects.

Tell the practice about drinking, weight changes, tiredness and itching, and current medication. When deciding on treatment, ask the vet to distinguish care needed for health from treatment aimed at coat appearance.

A hormone treatment trial should not replace diagnosis of a hormonal disease.

Agree when to return for review if the original pattern changes too. Bring the earlier diagnosis if another practice investigates the skin changes later.

Frequently asked questions

Is alopecia X the same as Cushing's disease?

Alopecia X can cause symmetrical hair loss resembling Cushing's disease. When needed, the vet rules out Cushing's with tests that assess adrenal function in more detail. Increased drinking and urination are consistent with suspected systemic hormonal disease.

Will hair lost from the flanks grow back?

After seasonal flank alopecia, the coat returns spontaneously in many dogs. In others, the flank remains permanently bald, while some have only one episode during their lifetime. However, regrowing hair may differ from the coat's original colour.

Must an otherwise healthy bald dog receive medication?

Flank alopecia affecting appearance alone can be left untreated. Monitoring can also be a sensible option for alopecia X instead of strong medication. Potential adverse effects must be weighed against the fact that this is usually a cosmetic disorder.

Can a dog with alopecia X be used for breeding?

Some Spitz breed-club guidance advises against breeding from affected dogs. The exact inheritance mechanism remains unknown. Diagnosis nevertheless requires exclusion of other causes of hair loss, so breeding decisions are not based on appearance alone.

Can I try melatonin myself?

Discuss melatonin with your vet after other causes of hair loss have been investigated. Diabetes may prevent its use for alopecia X. The medicine may also make a dog drowsy, so monitoring includes possible adverse effects.