Chapter 11 - Alopecia and 13 - Pigment Flashcards
Which breed is most commonly affected by pattern baldness?
Dachshund
Which anatomical sites are most commonly affected by pattern baldness?
Convex pinnae, periaural, ventrum, caudal thighs
With pattern baldness, is epilation normal or abnormal?
Normal
Which histopathological feature can help distinguish pattern baldness from endocrine alopecia or alopecia areata?
Minaturised hair follicles are seen with pattern baldness
Which dog breeds are most commonly affected by flank alopecia?
Boxers > Airedales, English bulldogs, Schnauzers
With flank alopecia, what is the characteristic appearance of hair follicles on histopathology?
‘Witches feet’ appearance to hairs
In dogs, telogen effluvium is seen most commonly with which chemotherapeutic agent?
Doxorubicin
Ischaemic dermatitis is thought to occur with traction/compression alopecia, which drug may be beneficial?
Pentoxifylline
Which breeds are commonly affected with rabies vaccine alopecia?
Min./Toy Poodle, Maltese, small long-haired dogs
How long after rabies vaccination does alopecia occur?
2-4 months
What is erythema ab igne?
Chronic, radiant heat dermatitis from prolonged, repetitive exposure to heat
Which neoplasia is most often associated with paraneoplastic alopecia in cats?
Pancreatic neoplasia
What other characteristic clinical signs is seen with paraneoplastic alopecia in cats?
Shiny skin
What do you see on histopathology of exfoliative dermatitis and thymoma?
Hydropic interface dermatitis with some apoptosis
Which enzymes most notably affect melanin colour and production?
Tyrosinase and tyrosinase-related proteins 1 and 2
Define poliosis
Premature greyness of hair
Define achromotrichia
Loss/absence of hair pigment
Where are lentignes seen in dogs?
Ventrum
What causes colour point cats to have dark points?
Temperature sensitive hair bulb tyrosinase that is inactivated at 35-37^C
Which breeds are prone to post-inflammatory melanotrichia?
Yorkies, Silkies, Bedlingtons, Old English sheepdogs and Poodles
Albinism is due a to a mutation in which gene?
Tyrosinase gene (normal melanocytes but they lack the tyrosinase needed for melanin synthesis)
What is the phenotype of Waardenburg-Klein syndrome?
Amelonotic skin and hair, deafness, blue or heterochromic irides
With Waardenburg-Klein syndrome, how does the genetic defect affect melanocytes?
Defect in migration and differentiation of melanoblasts which leads to no melanocytes
Which hair colour has the highest nutritional requirement for production?
Black
In which breed of cat is vitiligo reported?
Siamese
Which infectious disease can cause leukoderma in the absence of overt swelling or other lesions?
Leishmaniasis
Pinnal erythema in cats has been associated with administration of which antibiotics?
Enrofloxacin and ciprofloxacin
At which body site do vitiligo lesions initially develop in dogs?
Depigmented macules and/or patches initially developed on the face and were more often multifocal than focal. The gingiva and lips were the two most commonly affected regions.
Is dermal depigmentation present in the rare form of follicular vitiligo in dogs?
No - leukotrichia without leukoderma
Reported in Labrador retriever puppies
Is there a facial predominant form of vitiligo in horses and cats as in dogs?
Yes - although case reports are low in number
What are the key histopathological features of vitiligo?
- Loss of melanocytes from the epidermis and/or hair follicle.
- The epidermal architecture is normally retained but keratinocytes lack melanosomes in fully developed areas.
- Melanosomes are spilled to the superficial dermis (pigmentary incontinence), and sometimes the hair follicle peribulbar area, where they are incorporated in melanophages.
Where are lymphocytes found in vitiligo?
Minimal-to-mild numbers of lymphocytes are often present in the basal epidermal layer, especially near the junction of pigmented and nonpigmented epidermis; here lymphocytes are rarely observed adjacent to apoptotic melanocytes (“satellitosis”).
Melanocytes of the vertebrate integument are _____ cells of neural crest cell origin
dendritic
Melanin synthesis results in the generation of hydrogen peroxide and _______ intermediates which, if inappropriately processed, can damage the cellular components of epidermal melanocytes.
quinone
Name three factors known to regulate the quantity and quality of melanins produced by melanocytes
UV radiation
alpha-MSH
Agouti signal protein
Does alpha-MSH induce eumelanin or pheomelanin synthesis?
Eumelanin
Agouti signal protein induces pheomelanin
alpha-MSH binds to which receptor on melanocytes?
MSH receptor (MSH-R), also known as melanocortin 1 receptor (MCR-1)
Agouti signal protein acts as a competitive antagonist of α-MSH for the MSH-R
During its development, the melanosome acquires three gene-related melanogenic metalloenzymes, tyrosinase, and what else?
Tyrosinase-related protein 1 (Trp1) and and 2 (Trp2)
Tyrosinase is the most critical to melanogenesis!
Which mineral is essential for tyrosinase activity?
Copper
What is the is the metabolic precursor of melanin?
L-tyrosine (amino acid)
α-MSH is produced in melanocytes and which other epidermal cell?
Langerhans cells
Apart from alpha-MSH which other hormone can bind to MSH receptors in melanocytes and induce eumelanogenesis?
ACTH
Both enhance melanocyte proliferation, melanogenesis and melanocyte dendrite formation
How is melanin photoprotective?
It directly absorbs ultraviolet photons and reactive oxygen species (ROS) generated by the interaction of ultraviolet photons with membrane lipids and other cellular chromophores
Which breeds of dog are predisposed/commonly reported with vitiligo?
Rottweiler
Doberman pinscher dogs
Collies
Belgian Tervuerens
What is the median age of onset of vitiligo in dogs?
2 years
At which body site do cats develop lesions of vitiligo?
Nasal planum
Periocular
Footpads
Name the disease
arrow heads = lymphocytes
Vitiligo
Arrow = melanophages
Does vitiligo spontaneously resolve?
Yes - in some cases
Tham et al. (2019); which treatments should be used for vitiligo in dogs?
- Topical high potency steroids
- Tacrolimus
- Oral L-tyrosinase supplementation for 6 months
(4. NB-UVB Phototherapy may be promising option)
Do not guarantee repigmentation!
Which genes were found to be upregulated in vitiligo and VKH/UDS in dogs?
IFNG, TNF, PRF1, IL15, CTSW, CXCL10, and CCL5
Dog leukocyte haplotype (DLA)-DQA1*0020 has been associated with which disease?
Uveodermatological syndrome in American Akitas
Which breeds of dog are over-represented with UDS?
Akitas, Samoyeds and Siberian Huskies
What is the typical age and sex of dogs affected with UDS?
3.6 years
Males > females
Do ocular or cutaneous signs develop first in dogs with UDS?
Ocular in 85%
86% of dogs will have both within 6 months
What are the non-cutaneous signs of UDS?
- Blindness or poor/decreased vision 56%
- Uveitis 40%
- Conjunctivitis 18%
Lethargy, head tilt, reduced appetite, pica
Other than leukoderma and leukotrichia, what cutaneous signs have been reported in dogs with UDS?
- Erosions-ulcerations
- Alopecia
- Erythema
- Swelling of the nose (loss of architecture)
- Pruritus
- Hyperkeratosis of footpads
- Onychomadesis (loss of claws)
What is the distribution of skin lesions in dogs with UDS?
- Nasal planum 86%
- Periorbital skin/eyelids 74%
- Lips 65%
- Mouth/oral cavity, footpads and/or the genitalia (males) 23%
What are the histopath findings in canine UDS?
- Superficial perivascular inflammation that coalesces into lichenoid pattern that includes macrophages, lymphocytes, plasma cells and a variable number of neutrophils
- Exocytosis of lymphocytes into the lower epidermis blurs dermo-epidermal junction, but basal keratinocyte injury and loss is limited or absent.
- There is partial-to-complete loss of melanocytes
- Pigmentary incontinence
- Epidermal hyperplasia is normally seen with erosions, ulcers, neutrophil transmigration, patchy parakeratosis and/or crusting
Does initiating treatment within 1 month of the first clinical signs of UDS in dogs affect outcome?
Yes - early treatment = better outcome
Tham et al. (2019); what is the recommended treatment for UDS in dogs?
- Topical ophthalmic together with systemic GC at 2 mg/kg/day or higher.
- Other immunosuppressive therapies, such as azathioprine or ciclosporin, should be added if GCs therapy fail to induce the CR of signs
How do you describe the lesions of lentigo?
Macular melanosis
At what age do dogs develop lentigines and how do they progress?
Mature age
Develop in number and size over a few months then remain static
What is a differential for macular melanosis if the skin feels rough or thickened?
Epidermal nevi
Papilloma virus induced lesions (viral plaques)
At what age do cats develop lentigo?
<12 m
When do you see post-inflammatory melanotrichia (in Yorkshire terriers, silky terriers, Bedlingtons, OES and poodles)?
After healing of deep inflammation e.g. panniculitis, vaccine reactions, wounds, sebaceous adenitis (poodles)
A patch or plaque of grey-blue comedones should raise suspicion for which disease?
Demodicosis
Which drugs have been associated with hyperpigmentation reactions in dogs?
Ketoconazole
Minocycline
‘Snow nose’ occurs in which breeds of dog?
= decreased pigmentation of the nose in the winter (can be cyclic)
Siberian huskies
Golden retrievers
Labradors
BMDs
Mucocutaneous hypopigmentation can be seen in Dobermans and Rottweilers, how doses it differ from vitiligo?
It is present from birth and is static in nature
A temporary loss of pigment in Chow puppies that spontaneously resolves in 2-4 months is associated with a deficiency of which enzyme?
Tyrosinase
Acquired hypopigmentation of the nose and lips can occur in dogs after contact with what?
Rubber/plastic food bowls
Which drugs have been associated with hypomelanosis?
S/C injections and topical GCs S/C progestational drugs Ketoconazole Procainamide Potent antioxidants (dihydroquinone) Cabergoline
Reddish discolouration of the hair coat can be seen with which endocrinopathies?
Sertoli cell tumours and hyperoestrogenism > hypothyroidism and HAC
Which drugs have been reported to cause colour change to the skin?
Clofamizine - cat, red/orange
Enro-/ciprofloxacin - cat, pinnal erythema
Can melatonin implants prevent recurrence of seasonal flank alopecia in dogs?
No
