Canine non-inflammatory alopecia: What's new and what's old

I believe non-inflammatory alopecia in the dog is relatively common and can also be very frustrating. It must be differentiated from self-trauma and infectious causes. I am hoping this article will aid in clarification of some the conditions that cause non-inflammatory hair loss, and can help you make a proper diagnosis and reasonable treatment protocol.

Photo 1: With ischemic dermatopathy, lesions can be encountered around the eyes. Visual scarring is apparent with an active disease.

We will exclude hypothyroidism and hyperadrenocorticism from our discussion, as these two endocrinopathies are fairly straightforward and not difficult to diagnose. I will mention, however, that Cushing's disease is a fairly common cause of alopecia (or even post-clipping alopecia, which I will elaborate later), but canine hypothyroidism associated with alopecia is much less commonly seen.

Ischemic dermatopathy

This is a fairly well-recognized skin disease that includes several subtypes. The classical and originally described form is dermatomyositis (DM). This disease is genetically-based, immunologically mediated, and is seen almost exclusively in Shetland Sheepdogs and Collie breeds. The mode of transmission is autosomal dominant, with variable expression. It can occur at an early age in multiple members of a litter, or can be seen later in life as adult-onset type. Focal to more generalized alopecia with crusts, vesicles (rarely seen), erosions and ulcers on the face, around the eyes, pinnal margins, boney prominences, pressure point areas, and the tip of the tail are common locations for lesions (Photo 1). Many lesions are deep and focal scarring is not uncommon. It is also common to visualize scarring in areas of active disease. The muscle involvement usually is very mild and non-clinical. However, it can be severe especially in puppies and involve muscle atrophy, weakness and even mega-esophagus. The diagnosis is based upon results of skin histopathology, EMG's and muscle biopsies.

Photo 2: While fairly uncommon, localized rabies vaccine-induced ischemic dermatopathy still affects small breed dogs.

The treatment can include pentoxifylline, vitamin E, prednisone, azathioprine or cyclosporine. The cause is unknown, although certain investigators believe vaccine administration is implicated in the onset of skin lesions.

Localized rabies vaccine-induced ischemic dermatopathy is seen in certain small breed dogs (terriers, Bichons and poodles). It is fairly uncommon but occurs with some regularity in my practice (Photo 2). A patch of alopecia, with some hyperpigmentation and some crusts can be seen at the site of rabies vaccine administration (usually between the shoulder blades) one to six months after the vaccine was given. The lesion may resolve with or without scarring, may progress and enlarge or may progress to involve multifocal areas (the third subtype) on the entire body thus mimicking dermatomyositis. Diagnosis is made as in DM, and treatment may involve similar drug therapies as DM or may involve surgical removal (may be very difficult) and can also include cessation of vaccinations.

Photo 3: With pattern baldness hair starts to thin predominantly on the pre-auricular areas.

Pattern baldness

This is a fairly common skin condition that is considered to be completely cosmetic in nature. It is seen most often in Whippets, Greyhounds, Daschund, Boston terriers, Chihuahuas, and other small breed dogs. Hair begins to thin as early as six months of age, predominantly on the pre-auricular areas, head, ventral neck, chest and caudal thighs (Photos 3 and 4). It can be progressive and look striking, involving other locations until all areas become confluent, especially in older Daschunds. Some of the areas of alopecia can become hyperpigmented. Diagnosis is based upon clinical examination and/or results of skin histopathology. There is no recommended treatment. However, melatonin has shown some benefit in some cases.

Photo 4: Pattern baldness can begin as early as 6 months of age in some cases.

Follicular dysplasia

This is a quite common hair follicle disorder that definitely has a genetic basis, as seen by the marked breed predilection. Dobermans (blue and fawn colored), Rottweilers, Siberian Huskies, Malamutes, Chesapeake Bay Retrievers, Labradors, Portugese Water Dogs and others are predisposed.

Photo 5: Follicular dysplasia can be seasonal or cyclical int he Boxer and English Bulldog breeds. Alopecia can be seen symmetrically on the trunk, ventral neck or caudal thighs.

It can be seasonal or cyclical in the Boxer and English Bulldog breeds.

The condition starts farily early on in age, around 1 or 2 and is slowly progressive. Alopecia can be seen in various locations but mostly symmetrically on the trunk (lateral trunk and flank area), ventral neck or caudal thighs (Photo 5). Hyperpigmentation is uncommon and can be more readily seen in the flank areas in the Bulldog breed. Color dilution alopecia is a form of dysplasia seen in the Doberman breed, Yorkshire Terrier, Chihuahua, Saluki, Irish Setter and Chow Chow that has accompanying abnormal pigmentation with odd coat color. In the areas of alopecia, crusts, papules and pustules from pyoderma can complicate the condition. Diagnosis is made on clinical examination, trichograms (examination of hairshafts under light microsopy) and skin biopsy.

Treament is not recommended except for concurrent pyoderma.

Alopecia X

Alopecia X (growth-hormone/castration responsive dermatosis, adrenal sex hormone alopecia, pseudo-Cushing's) has to be the most frustrating area to discuss, as this condition is poorly understood and has many names! Classically, this was first described in the early 1980s at the University of Tennessee in the Pomeranian breed. The affected dogs were young adults and had striking alopecia on the trunk, ventral neck, caudal thighs, and lateral trunk. In the original studies in the affected Pomeranians, abnormal sex hormone results were seen with ACTH stimulation. The affected dogs had exaggerated and elevated levels of progesterone and certain androgens.

Photo 6: Alopecia X is not only frustrating, it is poorly understood. The alopecia can start at an early age and remain progressive.

Research in humans with a similar condition suggests a deficiency or partial deficiency in adrenal enzymes. Thus, at one point it was speculated in the dog a deficiency of 21- dehydroxylase was present resulting in abnormalities in steroidogenesis and ultimately abnormally high levels of certain adrenal gland sex hormones. Therefore, the term adrenal gland hyperplasia-like syndrome was also coined recently! Unfortunately, some normal appearing Pomeranians also had some of these abnormal hormonal levels and recent evidence suggests the condition may not be related to just elevated progesterones and androgens. Moreover, treatment response based upon sex hormone levels often fail. As a result, and in conjunction with insufficient data since this original study, there is a fair amount of confusion and controversy.

The alopecia can start at an early age and be progressive. Initially, alopecia may involve only the primary or guard hairs giving the dog a "puppy coat" appearance Photos 6 and 7, p. 16S). Affected areas can be very scaly and pustules and papules can also be seen. Diagnosis is made generally with skin histopathology but ruling out other conditions may be needed as well.

These can include hypothyroidism, Cushing's disease and follicular dysplasia. Treatments can include neutering, melatonin, oral methyltestosterone and even Lysodren. All have ocassionally resulted in partial or complete regrowth of hair but alopecia may redevelop while on therapy.

Post-clipping alopecia

This condition is relatively straightforward and occurs after areas on the dog are clipped or shaved. It is most commonly seen on the trunk or limbs (in areas that are mostly commonly clipped). Specific breeds are affected and include the Nordic breeds that are plush coated. These breeds include Siberian Husky, Samoyed, Malamute, Keeshond and also the Chow Chow, Labrador, and German Shepherd. Areas of alopecia are noted several months later after clipping was performed along with variable degree of hyperpigmentation.

Photo 7: Virtual complete lack of guard or primary hairs is evident on the lateral trunk of this adult Chow Chow.

One theory as to the cause is localized vasoconstriction occurs suddenly at the site, resulting in sudden arrest in the hair follicle cycle. It is also important to state the other causes of alopecia (primarily hypothyroidism, Cushing's and Alopecia X) all can manifest as post-clipping alopecia. Diagnosis is based upon clinical evaluation, skin histopathology and eliminating other causes of alopecia.

Aggressive rubbing or scraping of the affected areas can result in regrowth of hair. Affected dogs usually regrow hair in six to 12 months.

In conclusion, there are numerous causes of alopecia that are non-inflammatory in appearance, and this articles discusses and differentiates a portion of the more common ones. Pruritus and superficial bacterial folliculitis (pyoderma) are the more common causes of alopecia, so a complete history and good clinical examination with appropriate diagnostics are paramount in making a proper diagnosis.