Approach to alopecia Flashcards
Define alopecia?
= Loss of hair
Can be partial or complete
Primary
- Failure to grow normally
Secondary
- Grows normally but subsequently damaged or lost
What are the mechanisms of primary alopecia?
Start in anagen, growing hair, passes into catagen and then into telogen which is resting phase
Different hairs may be present at different phases depending on breed and area etc. at one time
Breed permanently in anagen – poodles, humans. They don’t have telogen, which is why they don’t malt
Most do malt – telogen hair, waits to fall out
How it can go wrong for primary alopecia on the picture.
Elongation – stuck in telogen
Define true and apparent alopecia?
True alopecia
Direct damage to hair follicle unit –> loss of whole hair follicle unit
Lose ENTIRE hair follicle unit
Apparent alopecia
Hair shaft damaged but not lost from hair follicle unit
Hair cropped short
Shaft is damaged and hair is not lost from follicle unit
Check a trichogram – look at distal tips
Broken off? But shaft looks normal? Probable pruritus – investigate as pruritus case.
What are the causes for alopecia?
Hair follicle inflammation (folliculitis (follicle inflame)/furunculosis (follicle ruptures releasing keratin into dermis, foreign body reaction)/bulbitis (inflame of hair bulb, usually autoimmune thing – rare))
–> Hair follicle unit damaged, hair drops out
Hair cycle abnormality
E.g. Endocrine disease
–> Hair stops growing
Hair morphological abnormalities
–> Hair malformed, breaks off – hair grows fine but is malformed and breaks off
Congenital Aplasia
–> Never grows
How does history and signalment affect the approach to the canine alopecic patient?
Age of onset
- <1yo: demodicosis, dermatophytosis, superficial pyoderma, congenital alopecia - Main things is infections that causes folliculitis – pyoderma, demodicosis and dermatophytosis – main 3 things that are common, must remember these
- Middle-aged/older: endocrinopathies, neoplasia
Breed
- Small terriers/boxers: predisposed to HAC
- Dachshunds: pattern baldness
- Doberman: dysplastic hair follicle diseases
Sex
- Entire male: Sertoli cell tumours, produce oestrogen and cause an endocrinopathy
- Entire female: post-partum telogen defluxion – if recently whelped, hair loss after whelping – common for bitches to lose their hair
General history
- PUPD
- suggestive of HAC
- Weight gain, lethargy
- suggestive of hypothyroidism
- Small hunting dogs (e.g. JRT)
- Trichophyton infection (rodent/hedgehog contact)
- Lesions on owner/in-contact animals
- dermatophytosis, ectoparasites
How can dermatological history help diagnose the cause of alopecia?
Lack of hair regrowth after clipping
- hypothyroidism, HAC, post-clipping alopecia. Post clipping alopecia is not fully understood, they will just not grow back – occasionally not ever, often like huskies or chows – so always talk to owners about this, especially if they are a show dog
Seasonality
- Recurrent flank alopecia
- Allergic pruritus – not technically a primary alopecia
Response to past treatment
- What has been done before?
Pruritus?
- If yes, investigate as per the pruritic animal – if there is pruritus, head down that route!!
How can physical examination help point towards the cause of alopecia?
General physical exam
Obesity, bradycardia:
- hypothyroidism
Unilateral testicular enlargement –>
- Sertoli cell tumour
Feminisation of male dog:
- Sertoli cell tumour
When is alopecia normal?
- Preauricular/pinnal alopecia of cats- All cats’ hair is thin in front of their eyes
- Sphinx cats – meant to look like this!!
- Irish water spaniels - bred to be alopecic on its ventral neck
Alopecia can be ‘normal’…
What are the most common causes of localised alopecia?
Demodicosis
Dermatophytosis – zoonotic!
Superficial pyoderma
Draw a diagram talking about acquired and congenital alopecia?
Alopecia can be present at birth
Congenital
Or it can be delayed onset – most will be acquired!
Coat colour linked follicular dysplasia
Colour dilution alopecia – in dogs where they have a dilute colour, the steel grey yorkie instead of black and tan etc.
Black hair follicular dysplasia
Non-coat-colour linked
Infection
Pyoderma
Dermatophytosis
Demodicosis
Leishmaniasis!
Endocrinopathies – must remember these
Hypothyroidism
HAC
Recurrent flank alopecia
Hyperoestrogenism in males
Hyperoestrogenism in females
Alopecia X
Other sex-hormone related
Iatrogenic
Anagen defluxion – can happen after steroids
Post-clipping alopecia
Miscellaneous
Follicular dysplasia
Telogen defluxion
Pattern alopecia
Sebaceous adenitis
Epitheliotropic
lymphoma
How can you tell difference between true and apparent alopecia?
Trichogram
Ease of epilation at periphery
Easily epilated –> true –Is it easier to peel out – this is TRUE ALOPECIA, a lot of endocrinopathies will do this
Requires some effort –> apparent
Broken distal tips –> apparent
How can trichograms tell us about cause of alopecia?
Bulb
Stage of growth?
Telogen predominates in endocrine disease
Shaft
Melanin clumping? Colour-linked follicular dysplasia
Dermatophyte spores? (lactophenol cotton blue helps demonstrate) often need special stain to see this
Follicular casts?
Distal tip
Broken? Traumatic damage/pruritus
Skin biopsy. What to sample?
- A variety of sites:
- Early lesions if possible
- Middle and periphery of expanding lesions – centre and middle
- Adjacent apparently normal area – to see whole expanse – can see if its spreading!
- Wedge biopsy across margin often useful
- mark direction of hair growth
Describe the alopecic pattern of endocrinopathies?
- All have similar ‘atrophic’ pattern
- Atrophy of:
- epidermis, hair follicles and sebaceous glands
- Orthokeratotic hyperkeratosis and follicular keratosis – lots of keratin
- Atrophy of:
- This pattern is seen in a variety of endocrine dermatoses - require hormonal assays to confirm their exact aetiology
Discuss skin changes in endocrinopathies?
- Skin changes often precede systemic signs in endocrine skin diseases
- Classic picture: Symmetrical non-pruritic alopecia
but
- often more subtle changes seen before this
e. g.
ceruminous otitis
recurrent microbial infection
generalised seborrhoea
- Usually proceed to hair loss within 6 months - usually see this animal on and off with other stuff before you see hair loss!
- Hair in affected areas usually dull, dry and epilates easily – telogen predominates
Hair regrowth can be
- Absent
- Very slow
- Abnormal e.g. woolly coat
Note the Incidence of clinical signs of hypothyroidism?
NB Dermatological involvement in approx 80% cases but often not initially alopecia
Discuss the incidence of clinical signs of hyperadrenocorticism?
Dermatological changes and very common with symmetrical alopecia
Commonly get secondary infections
Macular hyperpigmentation – big black spots
Discuss Hyperoestrogenism in males?
- Sertoli cell tumour (interstitial cell tumour, seminoma)
- Skin changes
- Alopecia, hyperpigmentation
- Gynaecomastia (enlargement of mammary glands)
- Linear preputial erythema (red line that runs along line of prepuce, not sure why)
- Attraction to other male dogs
- Occasional bone marrow suppression (oestrogens from neoplasm)
- Treatment: neuter (check for metastasis) – they don’t often metastasise
Discuss canine recurrent flank alopecia?
- Common!
- Cause - associated with photoperiod. Usually onset Nov-March, so over the winter
- Genetically influenced
- Boxers, Airedale, English Bulldog, Schnauzer, Rhodesian Ridgeback predisposed
- Mean age onset 4yr (range 1.5-11 years)
- Usually thoracolumbar, abrupt onset, well-demarcated alopecia
- Rule out hypothyroidism, HAC, other follicular dysplasias.
- endocrine tests
- biopsy
- Treatment
- Usually benign neglect… Normally regrows spontaneously in 3-8mo (range 1-14mo)
- Oral melatonin (unlicensed) at onset of alopecia? May or may not work
- Warn owner that 80% recur, though not always every year – If its gone, then comes back, likely to lose it again next year!
Discuss coat colour linked follicular dysplasia’s and colour dilution alopecia?
Colour dilution alopecia
- Associated with blue (dilute black) or fawn (dilute brown) coat colours
- Esp Doberman, Dachshund, Yorkshire terrier, whippet, greyhound
- Often secondary bacterial folliculitis
- Dystrophic change associated with dilute-colour hair only: large melanin granules and abnormal, weakened hair
- May lead to shaft fracture and alopecia
See image:
Normal (Top)
Large clumped melanin granules on hair shaft (bottom)
