Alopecia Flashcards
What is the difference between primary and secondary alopecia?
Primary alopecia = Failure to grow normally
Secondary alopecia = Grows normally but subsequently damaged or lost
What is the difference between true and apparent alopecia?
True alopecia = Direct damage to hair follicle unit => loss of whole hair follicle unit
Apparent alopecia = Hair shaft damaged but not lost from hair follicle unit => Hair cropped short
What are the mechanisms of primary alopecia?
Lack of stimulation of anagen phase (growth)
Abnormal growth factors => miniaturised/dysplastic hairs => break off/shed
Elongation of telogen phase (resting)
What are the causes of alopecia?
Congenital aplasia => never grows
Hair follicle inflammation (folliculitis/furunculosis/bulbitis) => damaged hair follicle unit
Hair cycle abnormality => hair stops growing (e.g., endocrine)
Hair morphological abnormalities => hair malformed, breaks off
Give examples of animals predisposed to diseases causing alopecia
Ringworm: very common in cattle, horses, cat, hedgehogs
Demodicosis, pyoderma – very common in dogs
Occult sarcoids – common in horses
Describe how age impacts the onset of alopecia
Immature animal:
- Infections (demodicosis/ dermatophytosis/ superficial pyoderma) - common
- Congenital alopecia - rare
Middle-aged/older: endocrinopathies, neoplasia, demodicosis
Give examples of how sex impacts the onset of alopecia
Entire female guinea-pig: ovarian neoplasia => alopecia
Entire male dog: Sertoli cell tumours => oestrogen production => alopecia
Give examples of how breed impacts alopecia
Small terriers/boxers: predisposed to hyperadrenocorticism (HAC)
Boxers, bulldogs: predisposed to recurrent flank alopecia
Dachshunds: pattern baldness
Staffies/bulldogs/Shar Peis: predisposed to demodicosis
Small hunting dogs (eg JRT): Trichophyton infection (rodent/hedgehog contact)
An alopecic animal displays with PU/PD and polyphagia, what is the likely cause?
HAC
An alopecic animal displays with weight gain and lethargy, what is the likely cause?
hypothyroidism
Give examples of when alopecia is ‘normal’
Preauricular/pinnal alopecia of cats
Sphinx cats
Irish water spaniels
Flank scent glands on hamsters
Normal coat shedding
If alopecic lesions are localised or multifocal/diffuse patchy what are the likely differential diagnoses?
Dermatophytosis
Pyoderma
Demodicosis
If alopecic lesions are symmetrical/diffuse what are the likely differential diagnoses?
Dermatophytosis
Pyoderma
Demodicosis
Endocrinopathies
Pattern alopecias
Follicular dysplasias
Trace element deficiency (cattle)
How can true and apparent alopecia be differentiated?
trichogram =>
Ease of epilation at periphery:
- Easily epilated => true
- Requires some effort => apparent
Broken distal tips => apparent
identify this lesion
Calcinosis cutis (HAC, dog)
identify this lesion
Comedones, skin thinning (HAC, dog)
identify this lesion
Epidermal collarettes, papules (pyoderma, dog)
identify this lesion
Draining sinuses, furunculosis (demodicosis, dog)
What initial and further tests should be done in an alopecia case?
Initial tests:
Skin scrapings - demodicosis
Dermatophyte investigations:
- direct microscopy/culture
- +/- Wood’s lamp
Trichograms
Further tests:
Cytology for pyoderma
Endocrine function tests
Skin biopsy
How can trichograms help diagnose the cause of alopecia?
Bulb:
- Stage of growth
- Telogen may predominate in endocrine disease
Shaft:
- Large melanin clumps e.g. in colour dilution alopecia (dog)
- Dermatophyte arthrospores/hyphae
- Follicular casts e.g. sebaceous adenitis (dog)
Distal tip:
- Broken
- Traumatic damage/pruritus
What can be seen on a skin biopsy in an alopecia case?
Folliculitis – e.g. bacterial, demodicosis, dermatophytosis
Atrophic changes => e.g. endocrinopathy
Follicular dysplasias
Autoimmune cause, e.g. Sebaceous adenitis, Alopecia areata
