Acquired alopecias mimicking endocrine skin disease (Parts 1 and 2) (Proceedings)

Hair is rich in protein and its growth requires adequate nutrition and the metabolic capability to process and utilize those nutrients. The hair follicle has three phases of growth: anagen, catagen, and telogen. The anagen phase is the period of active growth. The anagen hair bulb is active and deep in the dermis and the anagen hair is difficult to remove. Catagen is a short-lived transition phase after anagen where the follicle starts its involution process. In the telogen phase, there is no hair growth, the telogen bulb is high in the dermis, and the hair is easily removed.

Hair growth is genetically influenced, seasonally and topographically variable, and asynchronous. The genetic influence is obvious when one considers the coat differences between a Beagle and an Afghan hound. Seasonal variability, triggered primarily by alterations in temperature and light intensity, results in the noticeable shedding all animals do at least twice yearly. In fall (cooling temperatures and decreasing daylight), the hair cycle changes so there is minimal growth (10% anagen?) with maximal retention of telogen hairs. This allows the animal to develop its dense winter coat. In the spring (warming temperatures and increasing daylight), the follicles are activated and the new anagen hairs push out the old telogen coat resulting in the profound spring shed. Topographic variability is well characterized in humans where the hair cycle on the scalp, eyebrows, or sexual areas is different in the same individual. Differences in the number and/or affinity of various hormone receptors results in this topographical variability. In any given area of the body, adjacent hair follicles will be in a different phase of growth (asynchronous growth). This prevents shedding to baldness.

Evaluation of the Hair Loss Patient

As in all conditions, the minimum data base for a hair loss condition is the history and a complete physical examination for signs of internal disease. In addition to the data on the circumstance of the hair loss, one should determine the nature of the animal's coat before the hair loss started. In many cases, the owner will present an animal for hair loss of X-number of months duration when, in fact, the animal's disease has been going on much longer. The early signs, e.g., loss of luster, slower rate of hair growth, substandard coat for the breed, etc, often are overlooked. A helpful tool in chronic hair loss cases is to have the owner bring in some snapshots of the animal as a puppy or kitten, some around 1-year of age when the animal is developing its adult coat, and some in the first few years of life.

After the history and physical, the trichogram is the mandatory next step in a hair loss case. A small number, 10-15 typically, of hairs are plucked from the area of interest and placed on a microscope slide coated with mineral oil. All the hairs should be kept in the same orientation and separated slightly for better visualization. The slide is covered with a coverslip and examined at low power. Noted irregularities are examined at higher magnification. The number of samples to be collected and the best site(s) to collect them from varies from case to case. Typically, one or two samples is sufficient. When the hairs being lost appear normal grossly, sampling at the leading edge of the hair loss is most rewarding. When the condition revolves around broken hairs, e.g., dermatophytosis, the broken hairs are sampled.

In a trichogram from a normal dog or cat, there should be an admixture of primary and secondary hairs. The shafts are uniform in diameter until they start to taper at the tip. The size and structure of all primary hairs should be similar. Likewise, the secondary hairs should be similar one to another. Coloration of an individual hair may vary from the next depending on the coat color of the animal. The hairs should be straight in straight-haired animals and curly in curly-coated ones. The hairs should be separate from one another with little or no adherent follicular debris. In adult animals, there should always be an admixture of growth phases. In puppies and kittens, all the hairs are in the anagen phase of growth. In adults, anagen and telogen hairs always co-exist. Occasionally, a catagen bulb will be seen. At close inspection of the hairs, the cuticle, cortex, and medulla should be clear and sharply defined.

Persistent Noninflammatory Hair Loss

The conditions herein will persist from their onset unless medical or surgical treatments are undertaken.

      Endocrine Skin Diseases

           Structural Follicular Dysplasias

The term follicular dysplasia is used to describe a variety of hair loss conditions which are due to structural irregularities or defects in follicular anatomy, abnormal follicular production, or abnormal follicle cycling. With structural defects, the hair follicle is histologically abnormal and produces either no hair or abnormal hairs. With abnormal follicular production, there is no flagrant histological evidence of hair follicle disease but abnormal hairs are produced. In the cyclic dysplasias, there is histological evidence of hair follicle cycle disruption (catagenization of hair follicles) but the hairs produced are normal. Overlap in these three categories can be seen especially when the condition is very chronic in nature. These disorders probably have a genetic basis so they are seen in young animals and are symmetric in distribution. Some disorders involve most hair follicles while others are regionalized.

           Congenital Hypotrichosis or Alopecia

Recognized in various species and breeds within each species. Affected animals are born with hair loss or develop it within the first month or so of life. Hair loss can be accepted as normal (e.g., Mexican Hairless, American Hairless terrier). In most instances, it is considered a disease and can be symmetrically regionalized or generalized. In animals with ectodermal dysplasia, dental and ocular changes can accompany skin changes.

           Pinnal Alopecia

Most commonly recognized in the dog but can be seen in the cat. Onset of pinnal hair loss around 1 year of age. Hypotrichosis progresses to complete pinnal alopecia. Exposed skin hyperpigments quickly and markedly. Some suggestion that it may share the same etiopathogenesis as seasonal flank alopecia. Some claims that melatonin (0.5 mg/kg q12h) improves these animals.

           Pattern Baldness

Seen frequently in dachshunds, Boston terriers, and greyhounds but recognized in various other short-coated breeds. Regionalized in most dogs to post-auricular region, the ventrum, and posterior thighs. Normal puppy coat replaced with thinner then normal adult in the affected regions and those hairs are slowly lost with increasing age. Hair loss is rarely complete even in advanced case so differentiation from endocrine disease should be easy. Same etiopathogenesis as seasonal flank alopecia? Some claims that melatonin (0.5 mg/kg q12h) improves these dogs.

           Black Hair Follicular Dysplasia

Dogs are born normal but start to lose black hairs by weeks of age. Affected hairs lose luster prior to being lost. Focal or generalized.

           Color Dilution Alopecia

Recognized in animals (rare outside of the dog) with a diluted (blue or beige(fawn)) coat color. Not all dogs with a diluted coat color develop this condition. Onset of signs depends on the breed and degree of dilution. Dogs with a very dilute coat color (e.g., very light gray) lose hair early in adulthood. Nondiluted hairs (e.g., tan points in a Doberman) are not affected. Hair loss can be focal in dogs with bi- or tri-color coats or be generalized.Trichographically, affected hairs have very large pigment clumps (macromelanosomes) which disrupt the hair shaft anatomy and weaken it. These weak hairs break with trauma (e.g., friction, grooming) and result in hypotrichosis to alopecia. These broken hairs regrow for a certain period of time (can be years) but eventually the hair loss becomes permanent. During the hair loss phase, the animal is prone to a bacterial folliculitis. Some investigators have stated that treatment with retinoic acids improves the coat in these dogs. This therapy is very expensive and could not be expected to return the dog to normal. Beyond bathing to prevent follicular impaction and bacterial/yeast overgrowth, no treatment is likely to help these animals.

           Breed-specificFollicular Dysplasias

Structural defects in the hair shaft and hair follicle have been recognized in various different breeds. Although clinical details vary from syndrome to syndrome, the hair loss occurs in young dogs, usually is regionalized rather then generalized, and tends to be transient early on. With time, the hair loss becomes permanent. No effective treatments reported.

           Siberian Husky and Malamute

Onset at 3-4 months of age. Loss of primary but retention of secondary hairs. Coat color change to reddish brown.

           Doberman Pincher

Red or black dogs. Onset between 1 and 4 years of age. Flank and saddle region involved initially. With time, the hair along the dorsum is lost but retained elsewhere.

           Airedale Terrier, Boxer, English Bulldog, Staffordshire Terrier

Flank and saddle hair loss. May be cyclic or persistent from onset.

           Irish Water Spaniels, Portuguese Water Dogs, Curly-coated Retriever

Onset in puppyhood but rarely recognized (attributed to puppy shedding). Hair loss around face and over dorsum. Cyclic initially but eventually permanent.G. Trichorrhexis Nodosa: Common? Affected hair has focal weak spot which resembles two brooms pushed together. Hairs break at this point giving the coat an uneven appearance. Usually temporary (topical insult?) but can be permanent. Golden retrievers may be predisposed to the permanent form

           Trichoptilosis

Trichoptiotic hairs are those with split ends. All animals will have a small number of these hairs but no coat irregularity is recognized. When large number occur, the coat develops a disheveled look. In most cases, trichoptilosis is due to solar, chemical, and/or physical trauma to the hair shafts and is resolved by correcting the underlying cause. A permanent form has been recognized in the Golden retriever.

           Pili Torti

Affected animals have curly hairs when they should be straight. Whole body involved when off genetic origin. In acquired cases, not all hairs are affected and defect disappears with correction of the underlying condition.

           Shaft Disorder of Abyssinian Cats

Rare condition. Onion-like bulb appears in an otherwise normal hair shaft. Hair breaks at this point.

           Traction Alopecia

Uncommon to rare but easy to diagnose. Seen in breeds (e.g., Yorkshire terriers) where rubber bands are used to keep hair out of the dog's face or to prevent damage to a long show coat. Excessive traction is applied to hair follicle which results in temporary or permanent alopecia.

           Feline Acquired Symmetrical Alopecia

Symmetrical, apparently spontaneous hair loss is common in cats but most cases are traumatic in origin. The cat licks/chews/pulls normal hairs in response to some pruritic or psychogenic condition. In the rare case, the hair loss, typically on the caudal ventrum and medial thighs, is not traumatic in origin and the cat has no documentable endocrine disease. Hair regrowth seen with T4 or progesterone supplementation.

           Feline Paraneoplastic Alopecia

Many similarities with the acquired hyperfragility syndrome of the cat. Associated with liver or pancreatic carcinomas or other serious internal diseases. Gradual development of constitutional signs of illness with a sudden onset on hair loss on the limbs and ventrum. Hair loss in other frictional areas develops shortly thereafter. Exposed skin often develops a glistening appearance and Malassezia yeast are a common finding. Due to the advanced stage of illness of the cat by the time the hair loss is recognized, treatment is difficult.

           Alopecia areata

Recognized in most species but rare. Sudden onset of sharply demarcated, focal hair loss. May have one or more areas of involvement. Generalized (alopecia universalis) disease not recognized. If "exclamation point hairs" are seen on trichrography, the diagnosis is straightforward. Since these hairs are rarely seen, the diagnosis typically requires skin biopsy. Spontaneous hair regrowth (may take years) is typical when lesions are few in number and/or size. Regrown hairs usually are white.

           Pseudopelade

A recently recognized disorder of the dog and cat. The animal develops one to many well-circumscribed areas of noninflammatory alopecia. Generalized disease sparing the head and neck has also been recognized. In cats, onychomadesis is a consistent finding. Steroids are of no benefits. Some suggestion that cyclosporine or tacrolimus may be beneficial.

           Sebaceous adenitis

Dogs and cats with sebaceous adenitis usually have seborrheic skin before hair loss is recognized. Hair loss is due to shaft fracture because the hairs are stiffer then normal (follicular keratin adheres to and envelops the growing hairs (hair casts)) and break with grooming, etc. In some animals, especially the Visla, hair loss occurs without any obvious seborrhea. Numerous hair casts are seen trichographically. Diagnosis by biopsy since widespread excessive hair casting is seen in other conditions (e.g., demodicosis, vitamin A disorders (excess or deficiency), primary seborrhea).

           Lymphocytic Mural Folliculitis

A recently recognized condition of the cat and horse. One or more areas of spontaneous, asymptomatic hair loss where the exposed skin looks and feels normal. Possible etiologies include drug reaction, very early systemic lupus, or very early epitheliotrophic lymphoma.

           Granulomatous Folliculitis

A very rare, recently recognized condition when the hair follicle is involved in a granulomatous process with giant cells. No infectious agents visible. Endstage reaction to some eliminated infectious agent?

Transient Noninflammatory Hair Loss

      Gonadal Disorders of the Intact Female

Occurs in regularly cycling bitches. Some of these dogs will develop an androgen patterned hair loss (collar region, rump, perineum, ventrum) 6 to 8 weeks after estrus. The hair loss is associated with signs of overt pseudocyesis. When the pseudocyesis is treated or resolves spontaneously the hair will regrow spontaneously but a relapse can be expected at next estrus.

      Defluxion Disorders

The stress of disease, high fever, parturition, drugs, or any number of other "stressful" conditions can induce a defluxion which results in a temporary coat abnormality.

           Anagen Defluxion

The stress is short-lived or not too profound. During the stressful period, hair growth stops and a small defect or band occurs in anagen hairs. Telogen hairs are not affected since they are not growing. After the stress is removed, the hair continues its growth but the band weakens it and it breaks off, typically in 7 to 14 days. Because telogen hairs were not affected, the animal does not develop hair loss but rather the hairs are of very unequal lengths. Diagnosis is via trichrography. The coat will return to normal with no treatment.

           Telogen Defluxion

The stress is long-lived or intense. During the stressful period, hair growth stop and all the hair follicles on the body go into the telogen phase. When the animal returns to normal, all the follicles enter the anagen phase and there is a massive and widespread shed. Since all follicles on the body are involve, the hair loss occurs on the face, distal limbs, and in other areas not normally involved in other processes. Diagnosis is via trichrography where all hairs are in telogen, a state which does not exist in any other disorder. The coat will return to normal with no treatment.

      Follicular Arrest Disorders

For no know reason, some animals start to regrow hair after an area is clipped for a surgical procedure and then the regrowth abruptly stops. The hair regrowth restarts in 6 to 24 months and the dog maintains a normal coat thereafter.

           Post-clipping Alopecia

Reported most commonly in densely-coated dogs such as the Akita but is regularly seen in Labrador retrievers and other breeds. When these dogs are clipped for surgery, they fail to regrow the clipped coat. If one examines the area carefully, a uniform (peach fuzz( will be seen but the hairs do not reach normal length. If the clipped skin was wounded away from the surgery site (e.g., bone marrow biopsy), a tuft of normal hair will appear at the wound site. All other hairs on the animal's body remain normal. Trichrography of the (peach fuzz( shows catagen hairs.This condition is most common when the clipping was done after the fall shed. Most dogs regrow coat spontaneously at the following spring shed. Some dogs remain hairless for several years before regrowth is seen.

           Catagen Arrest

A very uncommon condition (Weimaraners predisposed?) where the dog spontaneously loses hair over the caudal dorsum. Like the dogs with post-clipping alopecia, a peach fuzz appears (catagenized hairs) but hair growth stops. Spontaneous regrowth at next shed period.

      Follicular Lipidosis of Rottweilers

A rare condition recognized in dogs of either sex less than one year of age. Hypotrichosis-to- alopecia of the tan points. Adjacent black hairs are not affected. Intercurrent thyroid disease may occur. Spontaneous improvement-to-resolution in all dogs.

      Medullary Trichomalacia

Recognized trichographically in many different dogs and cats and as a syndrome in German Shepherd Dogs. In the German Shepherd, the coat is involved in one to a few spots. The first recognizable irregularity is that the hairs in the affected area first "stand up" in a large tuft. Alteration in the medullary structure causes the hairs to lose their flexibility and then break off. Spontaneous regrowth occurs in all dogs but the initial event may or may not be followed by another episode. The trichographic abnormalities seen in the German Shepherd syndrome (medullary depigmentation, medullary swelling, and longitudinal splitting of the overlying cortex with hair shaft fracture) have been seen in many other breeds of dogs and in several cats. In these cases, the areas involved are more numerous or are generalized. In many instances the animal has some other skin disease or a metabolic abnormality and the trichomalacia disappears with the resolution of the other problem(s).

      Trichorrhexis Nodosa

Common? Affected hair has focal weak spot which resembles two brooms pushed together. Hairs break at this point giving the coat an uneven appearance. Usually temporary (topical insult?) but can be permanent. Golden retrievers may be predisposed to the permanent form

      Trichoptilosis

Trichoptiotic hairs are those with split ends. All animals will have a small number of these hairs but no coat irregularity is recognized. When large number occur, the coat develops a disheveled look. In most cases, trichoptilosis is due to solar, chemical, and/or physical trauma to the hair shafts and is resolved by co

      Excessive Shedding

All animals shed constantly but between the massive spring and fall sheds, the shedding is insensible. In some cases, heavy shedding is near constant and the rare animal can shed to obvious hair loss. Some animals just shed more then others and there is no medical basis for the shedding. Some animals when kept under near constant light, especially with quartz halogen or fluorescent lighting, appear to shed excessively because of the lighting. Return to the natural light cycle may slow the shedding.

      Seasonal Flank Alopecia

Seasonal flank alopecia is seen in many breeds but is most common in the Boxer, English Bulldog, and Airedale terrier. Hair loss occurs spontaneously in one season and the hair loss persist into the next season. As the name indicates, the hair loss occurs in the flank and saddle region and the exposed skin hyperpigments profoundly and quickly. Trichographically, numerous hair casts are seen but the hair shafts usually look normal. Some dogs experience only one episode but many do it repeatedly. In these latter dogs, some structural defects in the hair shafts may be seen trichographically. Some dogs, especially those with visible structural shaft defects, will eventually maintain their hair loss year-round.

Although there are numerous exceptions to the rule, males and females tend to lose hair in different seasons. Intact males tend to lose hair in the fall (after the fall shed), stay hairless all winter long, and regrow hair in the spring. Females, especially neutered ones, tend to lose hair in the early spring, stay hairless all summer long, and regrow coat in the late summer or early fall.Because of the striking association with changes in light intensity, the hair loss may be due to pineal influences. Abnormal photoperiods associated with "night owl" owners (especially if they have quartz halogen or fluorescent lighting) or abnormalities in melatonin production have been postulated. If either is true, correction of the trigger event (reversion to 12 hours light - 12 hours dark or melatonin supplementation (0.5 mg/kg q12h) should prevent further episodes. No treatment is needed for (nor effective in?) the current episode as regrowth will occur in a matter of months. If the sex of the animal is meaningful (sex hormone levels vary with melatonin levels), sex hormone supplementation or neutering may also impact the hair loss.

      Short Hair Syndrome of Silky Breeds

Rare condition of the Yorkshire and Silky terriers. Dogs have normal puppy coats but the adult coat on the body is shorter then breed standard. Some have had a long normal coat for several years while others never develop the long coat. The coat that is present is normal so it appears that something has altered the hair cycle so the anagen phase is too short to grow a long, flowing show coat. No known treatment.

      Feline Pinnal Alopecia

Spontaneous pinnal hair loss with spontaneous regrowth months later.

      Chemotherapy

Chemotherapeutic agents usually have minimal impact on the hair coat of animals. If an effect is seen, widespread telogen defluxion is most common. Doxorubicin (Adraimycin 7) is known to cause hair loss on the head. Similar, but less striking, hair loss is seen in some dogs being treated for Cushing's disease with ketoconazole.