An overview on congenital alopecia in domestic animals

Alopecia, that is, lack of hair in any quantity, is a frequent complaint of pet owners. Although mostly acquired, rare congenital forms of alopecia exist that are associated with abnormalities in hair follicle morphogenesis. Congenital alopecias can result in changes in quality or quantity of hair follicles and the hair fibres produced by them. They vary in terms of clinical presentation and mode of inheritance. Histopathology is usually needed in order to differentiate between a reduced number of otherwise normal hair follicles and qualitative hair follicle abnormalities. Although our understanding of the molecular mechanisms that drive hair follicle morphogenesis in mice and humans has significantly increased during the last decade, still very little is known about congenital alopecias in domestic animals. Because of their rarity and the general lack of knowledge about their pathophysiology, classification of congenital alopecias in domestic animals is still unsatisfactory. This article reviews hair follicle morphogenesis and its most important molecular mechanisms, and it discusses the various forms of congenital alopecia occurring in domestic animals that have been described in the literature, differentiating between hair follicle aplasia, hair follicle dysplasia (i.e. defects associated with hair follicle development and defects associated with hair shaft formation), and neuroectodermal dysplasias, the latter involving the hair follicle pigmentary system.     

Congenital alopecia in a Bichon Frise

A Bichon Frise pup had congenital alopecia. Histologic evaluation revealed the absence of hair follicles, arector pili muscles, sebaceous glands, and sweat glands. Unlike previously described cases of congenital ectodermal defect, this alopecia was not associated with any color pattern; the pup was white until it was 4 months old, at which time normal black and brown pigmentation developed independently of the alopecic pattern.     

Congenital anemia, dyskeratosis, and progressive alopecia in Polled Hereford calves

A new syndrome of anemia, alopecia, and dyskeratosis was identified in Polled Hereford calves in this study. Cutaneous changes included hyperkeratosis and hair loss around the muzzle and ear margins, which progressed to a generalized alopecia and hyperkeratotic dermatitis. Histologically, orthokeratotic hyperkeratosis with dyskeratosis of epidermal and follicular keratinocytes was present. Alopecia was correlated with dyskeratosis of Huxley's layer and an increasing proportion of follicles in the telogen phase of the hair cycle. Dermatitis was characterized by a mild dermal mononuclear cell infiltrate and mild lymphocytic perivascular dermatitis. The anemia present at birth was nonprogressive and was classified as normochromic and normocytic to macrocytic. Reticulocytosis was absent, but bone marrow was markedly hyperplastic. Nuclear cytoplasmic asynchrony of the rubricyte and metarubricyte stages occurred in the bone marrow. Abnormal rubricyte nuclei and maturation arrest at the late rubricyte stage were common. Cytologic features of the erythroid series are similar to those of type I congenital dyserythropoietic anemia of human beings. Genealogic features suggest that this is a primary hereditary defect. The mode of inheritance, however, remains to be determined.     

Alopecia in the horse – an overview

Dr Stannard explains different forms of alopecia in the horse with emphasis on the hair follicle and its function in the production of hairs. Both normal and abnormal patterns of hair growth and shedding in the horse are reviewed. Overviews of several specific hair follicle abnormalities, both inflammatory and noninflammatory, are discussed in detail with their clinical relevance. Some of the clinical entities covered in this section (linear alopecia and alopecia areata) are caused by immunological attack against normal structures and could have been placed in Immunologic diseases. However, because the clinical presentation for these entities is alopecia, Dr Stannard chose to include them in his notes on alopecia. Other inclusions in this section include cutaneous bacterial infections (e.g. pastern folliculitis and dermatophilosis) as well as fungal infections of the hair (dermatophytosis).     

Alopecia areata with lymphocytic mural folliculitis affecting the isthmus in a thoroughbred mare

A 13-year-old, thoroughbred mare was presented with an 8-year history of multifocal, generalized, noninflammatory alopecia and a 3-month history of alopecia, erythema and scaling of the white star on the forehead and muzzle. Histopathological examination of biopsy samples from multiple sites on the body (mane, neck, shoulder, flank and gluteal region) showed a subtle lymphocytic inflammatory infiltrate affecting and surrounding the anagen hair bulbs, consistent with a diagnosis of alopecia areata. The biopsy sample from the star on the forehead showed atrophic hair follicles with perifollicular and mural mononuclear folliculitis affecting the isthmus. Immunohistochemical staining with a CD3 marker confirmed the T-lymphocytic origin of the inflammatory infiltrate in all the samples. The concurrent presence of lymphocytic infiltration at the bulbar and isthmic level of the hair follicles in the same horse is unusual. This finding may represent a variation of the histological appearance of alopecia areata.     

Alopecia areata in Eringer cows

Alopecia areata is a hair loss disorder in humans, dogs and horses with a suspected autoimmune aetiology targeting anagen hair follicles. Alopecia areata is only sporadically reported in cows. Recently, we observed several cases of suspected alopecia areata in Eringer cows. The aim of this study was to confirm the presumptive diagnosis of alopecia areata and to define the clinical phenotype and histopathological patterns, including characterization of the infiltrating inflammatory cells. Twenty Eringer cows with alopecia and 11 Eringer cows without skin problems were included in this study. Affected cows had either generalized or multifocal alopecia or hypotrichosis. The tail, forehead and distal extremities were usually spared. Punch biopsies were obtained from the centre and margin of alopecic lesions and normal haired skin. Histological examination revealed several alterations in anagen hair bulbs. These included peri‐ and intrabulbar lymphocytic infiltration, peribulbar fibrosis, degenerate matrix cells with clumped melanosomes and pigmentary incontinence. Mild lymphocytic infiltrative mural folliculitis was seen in the inferior segment and isthmus of the hair follicles. Hair shafts were often unpigmented and dysplastic. The large majority of infiltrating lymphocytes were CD3⁺ T cells, whereas only occasional CD20⁺ lymphocytes were present in the peribulbar infiltrate. Our findings confirm the diagnosis of T‐cell‐mediated alopecia areata in these cows. Alopecia areata appears to occur with increased frequency in the Eringer breed, but distinct predisposing factors could not be identified.     

Feline paraneoplastic alopecia

A 14-year-old neutered female cat was presented for a second opinion regarding hair loss, anorexia, and lethargy. Examination revealed alopecia of the ventral chest, abdomen, axilla, and groin. The footpads were encrusted. The liver was enlarged and nodular. Investigation revealed an enlarged liver with multiple nodules, and small and atrophic hair follicles. Paraneoplastic alopecia due to hepatocellular carcinoma was diagnosed and subsequently confirmed postmortem.     

Follicular dysplasia in two cows

The histological features of a follicular dysplasia with pigmentary changes is reported in two adult cows, one a black Brangus-cross and the other a black Angus. Adult onset of diffuse alopecia was present in both cows. Skin biopsies exhibited follicular distortion and atrophy, with melanin clumping in follicular epithelium, hair bulb matrix cells, hair shafts, and infundibular keratin. Both animals were clinically normal apart from the alopecia. This report confirms and expands on the infrequently reported syndrome of follicular dysplasia in cattle.     

Endocrine alopecia in a miniature poodle

Hypothyroidism and concurrent sex hormone imbalance associated with alopecia was diagnosed in a 5 year-old entire male Miniature Poodle. The dog had a 3-year history of alopecia, seborrhoea and recurrent superficial pyoderma. Abnormal thyrotropin releasing hormone stimulation test results supported a diagnosis of hypothyroidism. Partial hair regrowth occurred after interstitial cell tumours, which were present in both testicles, were removed by castration. Complete hair regrowth, however, occurred only after thyroid hormone supplementation. This case highlighted difficulties which may be encountered when interpreting serum hormone concentrations and endocrine function tests.     

Alopecia and dermatopathy of the lower back following pelvic fractures in three cats

Abstract   An alopecia and dermatopathy following pelvic fractures associated with vehicular trauma is reported in three cats. The animals presented 3–4 weeks post injury with acute hair loss, glistening appearance of the skin and erosions involving the lower back. Histological examination revealed atrophy of the hair follicles and adnexal structures and follicular telogenization, dermal fibroplasia and mild lymphocytic infiltrate, fibroplasia and inflammation in the panniculus. Vascular damage secondary to the external trauma to blood vessels supplying the skin over the lumbar region and subsequent ischaemia may represent the pathomechanism of this type of alopecia. Focal permanent hair loss can be expected.     

Anti‐isthmus autoimmunity in a novel feline acquired alopecia resembling pseudopelade of humans*

Pseudopelade is a primary scarring (cicatricial) alopecia of humans characterized by lymphocyte‐rich inflammation centred around the hair follicle isthmus. Lymphocyte folliculotropism is associated with isthmus apoptosis and, ultimately, follicular destruction and dermal fibrosis. In a cat, an acquired alopecia was diagnosed as pseudopelade based on the following criteria: (i) an adult‐onset, patchy to diffuse nonpruritic hair loss; (ii) an early folliculo‐destructive phase in which lymphocytes and dendritic cells accumulated in and around the follicular isthmus; and (iii) a late stage in which the lower segments of hair follicles underwent atrophy and were replaced by fibrosing tracts. Additionally, immunological investigations characterized the cytotoxic phenotype of isthmotropic lymphocytes and demonstrated the presence of circulating IgG autoantibodies specific for multiple follicular antigens. Altogether, the results of the present study suggest an immune‐mediated pathogenesis for this case of feline pseudopelade, similarly to that causing alopecia areata in humans and other mammalian species.     

Resolution of paraneoplastic alopecia following surgical removal of a pancreatic carcinoma in a cat

A 13-year-old female neutered domestic longhaired cat was presented with a five-month history of progressive weight loss and bilaterally symmetrical alopecia of the ventrum, limbs and perineum. The alopecic skin had a shiny appearance and hair in the non-alopecic areas was easily epilated. Fine needle aspirate cytology of a palpable cranial abdominal mass revealed it to be of epithelial or glandular origin. A pancreatic mass was excised by left pancreatectomy during exploratory laparotomy, and histopathology and skin biopsies confirmed a diagnosis of pancreatic carcinoma with concurrent paraneoplastic alopecia. No evidence of metastases was found on liver and lymph node biopsies. At re-examination 10 weeks after surgery, the hair had fully regrown. Skin signs recurred after 18 weeks and metastatic spread of the tumour was confirmed on postmortem examination. This case confirms that paraneoplastic alopecia associated with internal malignancies is a potentially reversible process if the internal neoplasm is excised.     

Morphologic and immunologic characterization of a canine isthmus mural folliculitis resembling pseudopelade of humans

The clinical, histopathologic and immunopathologic features of a novel form of isthmus mural folliculitis in dogs, which resembles pseudopelade in humans, were characterized. Clinically, dogs exhibited variably distributed foci of alopecia that persisted without treatment or did not respond to immunosuppressive therapy. Histopathologically, mixed mononuclear cell infiltrates, largely lymphocytes, infiltrated the follicular isthmus. Occasionally, inflammation extended above and below the follicular isthmus but did not involve the hair bulb or the epidermis. Severe follicular atrophy and variable atrophy of sebaceous glands occurred in all dogs. Folliculotropic lymphocytes exhibited most commonly CD3 and CD8 (cytotoxic T cells). Autoantibodies specific for the lower hair follicle were detected in the serum of affected patients. Western immunoblotting demonstrated binding of these antibodies to multiple follicular keratinocyte proteins, including hair keratins and trichohyalin. Lack of hair regrowth (in contrast to canine alopecia areata), as well as location of inflammation and extreme atrophy of adnexal units are similar to findings seen in human pseudopelade.     

Generalized alopecic and cystic dermatosis in a cat: a counterpart to the hairless mouse phenotype or a unique congenital dermatosis?

A 2-year-old, male neutered, domestic semi-long-haired cat was presented with a 1.5-year history of progressive, initially nonpruritic alopecia and malodorous greasy exudate affecting the distal extremities, trunk and neck but sparing the head and tail. The extensive alopecia and 'seborrhoea' were associated with severe thickening of the skin and fold formation on the dorsal head and distal extremities as well as the lateral thorax and abdomen. The hair was easily epilated, numerous milia were seen on the ventral abdomen and the caudal and lateral thighs, and mild paronychia was present. Histopathological examination of skin biopsies revealed marked cystic dilation of hair follicles and sebaceous glands with follicular hypoplasia, infundibular hyperkeratosis and variable associated inflammation. Systemic glucocorticoid therapy in combination with topical washes with chlorhexidine and miconazole resulted in a marked improvement and some hair regrowth, but the cat was subsequently lost to follow-up. The dermatosis resembles a number of conditions in other species, but it is not clear whether it is a counterpart to the hairless mutant mouse or is a unique dermatosis.     

Oestrogen receptor antagonist and hair regrowth in dogs with hair cycle arrest (alopecia X)

An oestrogen receptor pathway that regulates the telogen-anagen hair follicle transition in mice has been described. The purpose of this study was to investigate whether fulvestrant, a pure oestrogen receptor antagonist, would cause hair regrowth in Pomeranian dogs with hair cycle arrest (alopecia X). Eleven Pomeranian dogs with hair cycle arrest were randomly assigned to receive two intramuscular injections of either 10 mg kg(-1) fulvestrant (n = 6) or an equal volume of saline (n = 5) 1 month apart. Complete blood count, chemistry panel, and urinalysis were monitored prior to the first injection and monthly for 2 months. Dogs were evaluated each month for degree of hair growth, percentage of body affected, and quality of new hair growth. Three control dogs received fulvestrant after the completion of the study. In addition, one control dog and one treatment dog received two subcutaneous injections of 20 mg kg(-1) fulvestrant 1 month apart. No dogs that received 10 mg kg(-1) fulvestrant had any evidence of hair regrowth. The control dog that received 20 mg kg(-1) fulvestrant had substantial hair regrowth 1 month after the first injection. No adverse effects from the treatment were noted. Fulvestrant does not appear to be a feasible treatment for dogs with hair cycle arrest (alopecia X) when administered intramuscularly at 10 mg kg(-1). A higher dose of fulvestrant requires more investigation but may be cost-prohibitive.     

Oestrogen-induced alopecia in a bitch

An 8-year-old, spayed female Labrador Retriever, which had been treated with oestrogens for urinary incontinence, developed non-pruritic, bilaterally-symmetrical alopecia and skin hyperpigmentation, with enlargement of mammary glands and vulva. Skin biopsy changes were consistent with an endocrine alopecia, hypothyroidism and hyperadrenocorticism were excluded by hormonal tests. Oestrogen-induced alopecia was suspected and hormonal treatment withdrawn. Two months later, hair regrowth was almost complete and genital changes were lessened.     

Seasonal flank alopecia in ovariohysterectomized dogs

Recurrent seasonal flank alopecia was recognized in 5 ovariohysterectomized female dogs. The dogs first developed hair loss between 1 1/2 and 4 1/2 years of age. The hair loss began in March or April (spring) and spontaneously resolved in July or August. The dogs were otherwise healthy, and no cause for the condition could be determined.     

Growth hormone responsive dermatosis in three dogs

Growth hormone responsive dermatosis was diagnosed in three dogs. Each dog showed truncal hair loss, and two animals also had alopecia of the ventral neck, tail and thighs. The diagnosis in two cases was made by eliminating other causes of hormonal alopecia and demonstrating little increase in plasma growth hormone concentration after the intravenous administration of xylazine. All three dogs responded favourably to the subcutaneous administration of recombinant human somatotropin.     

Growth hormone responsive dermatosis in three dogs

Growth hormone responsive dermatosis was diagnosed in three dogs. Each dog showed truncal hair loss, and two animals also had alopecia of the ventral neck, tail and thighs. The diagnosis in two cases was made by eliminating other causes of hormonal alopecia and demonstrating little increase in plasma growth hormone concentration after the intravenous administration of xylazine. All three dogs responded favourably to the subcutaneous administration of recombinant human somatotropin.