Derm - Alopecia Flashcards
What makes up the structure of the hair follicle?
Hair bulb
Arrector pili muscle
Sweat gland
Sebaceous gland
What are the three stages of the hair cycle?
Anagen - active growth
Catagen - involution of the hair shaft
Telogen - no growth (until anagen displaces the old hair for a new one)
What do anagen hairs look like?
Rounded bulb like appearance
What do telogen hairs look like?
Tapered brush like root
What causes hair growth?
Keratinocytes form the hair shafts from the matrix of the hair bulb
These then differentiate into hair shaft and inner root sheath
Stem cell region replace epidermal keratinocytes
Daughter cells migrate up and out of the hair follicle
What molecules control the development of the hair follicle? What are they synthesised by?
Morphogens
Synthesised by tissue cells adjacent to the follicle or hormones
What are the 3 main pathogenetic mechanisms that result in alopecia?
- Destruction of normally growing hair follicles and hair shafts
- Abnormalities of the hair cycle causing atrophy and regression of hairs
- Abnormalities of the hair follicle/shaft causing structural defects
What are some causes of destruction of normally growing hair follicles?
Traumatic alopecia - self trauma
Folliculitis - staph infection, demodex, dermatophytosis
Inflammatory alopecia - vascular diseases, sebaceous adenitis, neoplasia
How do vascular disease cause alopecia?
Loss of blood supply to skin results in damage to hair follicle
How does sebaceous adenitis cause alopecia?
Inflammation of sebaceous gland spills over into hair follicle
What is the most common cause of abnormal hair cycles causing hair follicle atrophy?
Endocrinopathies
What is the most common cause of abnormal hair follicle/shaft developent?
Follicle dysplasia/dystrophy
Associated with certain breeds, coat types/colours
What is dermatophytosis?
Ringworm
How does dermatophytosis cause alopecia?
Arthrospores adhere to keratinocytes and cause microtrauma to the skin
Then invades epidermis
Enzymes breakdown keratinocytes
What is the incubation period for dermatophytosis?
1-3 weeks
What is the organism that causes dermatophytosis most commonly in cats and dogs?
Microsporum canis
What is the organism that causes dermatophytosis from exposure to rodents?
Trichophyton
What type of cat is particularly susceptible to dermatophytosis becuase it cant mount a good immune response?
Persian cats
What are the clinical signs of dermatophytosis?
Alopecia
Scale
Central healing
Folliculitis and furunculosis
How can you diagnose dermatophytosis?
Fungal culture of hair and scale samples by the lab
PCR - quick but too sensitive, false positives possible
Wood’s lamp
How can you collect samples to diagnose dermatophytosis?
Brush affected areas
Plucking
Scraping
How does a Wood’s lamp work for diagnosing dermatophytosis?
Examine animal in a dark room to show fluorescence in the lesions/hair
Only works for M. canis
Pluck the hairs htat light up
How can you treat dermatophytosis?
Animals can self cure
Topical therapy can reduce transmission
Should you clip animals with dermatophytosis?
May help to reduce environmental and host load but may spread disease in the affected animal
Infection can spread up to 6cm from obvious lesions
