The approach to alopecia 2 Flashcards
An abnormal hair cycle leads to?
Hair cycle arrest
Abnormal formation/synthesis of the hair leads to ?
Hair synthesis defects
Name the 5 parts of the hair cycle
- Anagen
- Catagen
- Telogen
- Exogen
- Kenogen
Describe anagen in the hair cycle
Growing phase, where the hair shaft is produced deep in the dermis
Describe catagen in the hair cycle
Transition phase with regression of the lower part of the hair follicle, no more growth
Describe telogen in the hair cycle
Quiescent/resting phase
Describe Exogen in the hair cycle
Release and shedding of the hair
In primary alopecia most of the hair follicles are in which part of the hair cycle?
Telogen
• Lack of anagen induction
• Impaired anagen promotion
• Premature catagen
Give 3 examples of endocrinopathies which cause hair cycle arrest
- Hyperadrenocorticism
- Hypothyroidism
- Hyperoestrogenism (functional testicular/ ovarian tumours)
What are the clinical features of alopecia due to endocrinopathies?
- Symmetrical to generalised alopecia: typical to affect the trunk
- Dull and dry coat (± scale)
- Comedones
- Hyperpigmentation
- Atrophic skin
- Poor wound healing
Describe the pathophysiology of hyperadrenocorticism
- Glucocorticoids effect on the skin -> catabolic and antimitotic effect
- Decreased mitoses -> thinning, delayed wound healing, pilosebaceous atrophy
- Inhibition of fibroblast proliferation, collagen and matrix substance production -> thinning, fragile vessels
What signs are seen in a patient with hyperadrenocorticism
- Truncal alopecia
- Comedones
- Skin atrophy and striae (wrinkles
- Prominent blood vessels
- Calcinosis cutis
Describe Calcinosis cutis
- Inorganic, insoluble mineral salts are deposited in the dermis, subcutis or, rarely, the epidermis
- ++ on collagen and elastin fibers in the dermis
- Occurs with hyperadrenocorticism if steroid treatment is given for too long/too much
- Initially start as small papules that increase in number and fuse to form a plaque
- Lesions are very hard
Describe the pathophysiology of hypothyroidism
- Thyroid hormone effect on the skin -> stimulation of cytoplasmic protein synthesis and increase tissue oxygen consumption
- Initiation of anagen phase, wound healing
- Decrease cell apoptosis –> prolonged anagen phase
- Promote matrix cell proliferation
What signs are seen in a patient with hypothyroidism?
- Truncal and extremity alopecia
- Dull hair coat and hair loss on areas of friction
- Myxoedema ‘tragic’ facial expression
- Weight gain
- Lethargy
- Heat seeking
- Rat tails: hair loss and hyperpigmentation
What are the causes of Hyperoestrogenism?
- Functional testicular neoplasia (++ Sertoli cell tumour +/- interstitial cell tumors (rarely seminomas)
- ++ cryptorchid testes
- Rarely caused by ovarian tumors
What are the effects of oestrogens on the hair cycle?
- Initiation and promotion of catagen by induction of apoptosis
- Inhibition of anagen onset -> longer telogen phase
What is telogen defluxion and when does it occur?
Sudden loss of hair
- 1-3 months after a stressful event e.g. pregnancy, lactation, severe illness, surgery, shock
What is anagen defluxion and when does it occur?
Sudden hair loss - Chemotherapy - Severe illness Loss of whiskers Damage to growing hair/follicle
Describe the features of feline paraneoplastic alopecia
- Pancreatic and bile duct carcinomas, neuroendocrine pancreatic tumour, hepatosplenic plasma cell tumour
- Alopecia ventrum and legs
- Skin shiny and translucent – not fragile
- Surgical excision can be curative if done in the early stages
Alopecia X occurs in which breeds?
Plush coated e.g. Pomeranians, chow chows
What are the clinical signs of alopecia X?
- Primary hairs lost first (puppy coat), later complete alopecia and hyperpigmentation
- Dull, dry coat - hair loss in frictional areas
- Truncal alopecia and hyperpigmentation, spares extremities
- Dog otherwise well (cosmetic disease)
What are some types of recurrent flank alopecia?
- Seasonal
- Linked to changes in day length
- Geographic-shaped alopecia in the thoracolumbar area
Describe the features of injection alopecia
- Unknown pathogenesis: Follicular atrophy with no inflammation
- Focal alopecia +/- hyperpigmentation & atrophy
- Usually local but may be remote from injection
- Glucocorticoids, vaccines (esp. rabies)
Describe congenital alopecia
- Defect in hair follicles
- Often associated with adnexal, epidermal, dental and nail defects (ectodermal dysplasia)
- Dominant, recessive, X-linked
Which breeds are affected by congenital alopecia?
Hairless breeds e.g. Mexican hairless, Chinese crested, Sphynx
Follicular dysplasia is a familial disorder that affects which breeds?
Irish water spaniel, Portuguese water dog, curly coat retriever, Airedale, others
‘Bald thigh syndrome’ affects which breeds?
Greyhounds and other sighthound breeds (Whippets, Galgo Español, and Magyar Agár)
Describe the features of ‘bald thigh syndrome’
- Bilateral hair loss on the caudal and lateral thighs
- Alopecia may extend to the distal hind legs, the ventral abdomen and the chest and the ventral neck
- May wax and wane
Describe black hair follicular dysplasia
- Familial disorder
- One or more genetic defects in melanisation
- Defect in pigmentation and hair formation
- Progressive changes
- Born normal, coat changes by 4 weeks
- Black hairs become dull
What are some methods of diagnosing hair synthesis defects?
- History and clinical signs: Breed, Distribution, Coat colour
- Trichogram
- Rule out endocrinopathies
- Skin biopsy and histopathology
