TRICHOGRAM
WHEN DO I DO IT?
- In every patient with alopecia
- To look for broken hair tips when one suspects self-induced alopecia
- To determine if hairs are in anagen or telogen phase (the interpretation of ratios of telogen hairs to anagen hairs in dogs is breed and season-dependent and exact ratios have not been established)
- When dermatophytosis is suspected
- To identify dogs with color dilute haircoats
- As an alternative to a deep skin scraping when Demodex is suspected
WHAT CAN I FIND
- Broken off hair tips → caused by self-trauma
- Tapered hair tips → hair loss is caused by events within the follicle e.g. endocrine disorders or inflammation involving the hair follicle
- Hairs in anagen (growing) phase → roots of anagen hairs are rounded, curled, bent and often smooth and pigmented
- Hairs in telogen (resting) phase → roots of telogen hairs are lancet-shaped and lack pigmentation, although the base of the hair may show a roughened or brush-like edge
- The presence of numerous anagen phase hairs should decrease the suspicion for an endocrinopathy
- In the case of dermatophytosis, affected hairs are covered with spores and penetrated by hyphae
- Color dilution alopecia→ melanin is clumped in the hair shaft
What do I need?
- Forceps/hemostat or rubber covered clamp, mineral oil, slide, cover slip, microscope
How do I do it?
- Pluck a small number of hairs in a partially or completely alopecic area using forceps/clamp in direction of hair growth; hold the forceps/clamp close to the skin surface and grasp all hair shafts which emerge
- Put a drop of mineral oil onto a slide, place the hairs in parallel order on the mineral oil, separate them to evaluate roots and tips adequately
- Cover hairs with a cover slip and evaluate with the microscope
Tip
- Cover the tips of your forceps or clamp with rubber or silicon sleeves to avoid crushing or breaking the hair shafts.
- You can also use the trichogram technique to look for Demodex mites in affected areas that are difficult to scrape (e.g. close to the eye, pododermatitis). Ideally a 1-2 cm2 area will be plucked, the same area as with a skin scraping.
- You might find Demodex mites hanging on the hairs or sometimes hiding behind them. Only positive results are diagnostic.
- You can also find lice, Cheyletiella mites and their eggs.
abscess
A discrete swelling containing purulent material, typically in the subcutis
Perianal abscess in a dog
alopecia
Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma
Extensive alopecia secondary to cutaneous epitheliotropic lymphoma
alopecia (“moth-eaten”)
well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis
“Moth-eaten” alopecia secondary to superficial bacterial folliculitis
hemorrhagic bullae
Blood-filled elevation of epidermis, >1cm
Interdigital hemorrhagic bulla in a dog with deep pyoderma and furunculosis
comedo
dilated hair follicle filled with keratin, sebum
Comedones on the ventral abdomen of a dog with hypercortisolism
crust
Dried exudate and keratinous debris on skin surface
Multifocal crusts due to pemphigus foliaceus
epidermal collarettes
Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles
Epidermal collarettes in a dog with Staphylococcus superficial bacterial folliculitis
erosion
Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.
Erosions in a dog with vasculitis
erythema
Red appearance of skin due to inflammation, capillary congestion
Erythema in a dog with cutaneous drug eruption
eschar
Thick crust often related to necrosis, trauma, or thermal/chemical burn
Eschar from physical trauma
excoriation
Erosions and/or ulcerations due to self-trauma
Excoriations in a cat with atopic dermatitis
fissure
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
Fissures of the footpads in a dog with superficial necrolytic dermatitis
fistula
Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues
Perianal fistulas in a dog
follicular casts
Accumulation of scale adherent to hair shaft
Follicular casts surrounding hairs from a dog with hypothyroidism
hyperkeratosis
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
Idiopathic hyperkeratosis of the nasal planum (left) and footpads (right)
hyperpigmentation
Increased melanin in skin, often secondary to inflammation
Inflammatory lesions (left) resulting in post-inflammatory hyperpigmentation (right)
hypotrichosis
Lack of hair due to genetic factors or defects in embryogenesis.
Congenital hypotrichosis in chocolate Labrador puppies.
lichenification
Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture
Lichenification of skin in a dog with chronic atopic dermatitis and Malassezia dermatitis
macule
Flat lesion associated with color change <1cm
Pigmented macule (left) Erythematous macule (right)
melanosis
Increased melanin in skin, may be secondary to inflammation.
Post inflammatory hyperpigmentation of this dog’s thigh
miliary
Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis
Miliary dermatitis in a flea allergic cat
morbiliform
A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas
Morbiliform eruptions in a dog with a cutaneous drug reaction
onychodystrophy
Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia
Onychodystrophy in dog with chronic allergies
onychogryphosis
Abnormal claw curvature; secondary to nail bed inflammation or trauma
Onychogryphosis in a dog with symmetric lupoid onychodystrophy
onychomadesis
Claw sloughing due to nail bed inflammation or trauma
Onychomadesis in a dog with symmetric lupoid onychodystrophy
onychorrhexis
Claw fragmentation due to nail bed inflammation or trauma
Onychorrhexis in a dog with symmetric lupoid onychodystrophy
onychoschizia
Claw splitting due to nail bed inflammation or trauma
Onychoschizia in a dog with symmetric lupoid onychodystrophy
patch
Flat lesion associated with color change >1cm
Hypopigmented patch (left), erythematous patch (right)
petechiae
Small erythematous or violaceous lesions due to dermal bleeding
Petechiae in a dog with cutaneous vasculitis
phlebectasia
Venous dilation; most commonly associated with hypercortisolism
Phlebectasia and cutaneous atrophy due to hypercortisolism in a dog
plaques
Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration
Plaques in a cat with cutaneous lymphoma
pustule
Raised epidermal infiltration of pus
Pustules on the abdomen of a dog with superficial staphylococcal pyoderma.
scale
Accumulation of loose fragments of stratum corneum
Loose, large scales due to ichthyosis in a Golden Retriever
scar
Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues
Scarring (right) following the healing of an ulcer (left) in a dog with sterile nodular dermatitis
serpiginous
Undulating, serpentine (snake-like) arrangement of lesions
Serpiginous urticarial lesions on a horse
telangiectasia
Permanent enlargement of vessels resulting in a red or violet lesion (rare)
Telangiectasia in a dog with angiomatosis
ulcer
A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.
Ulcerations of the skin of a dog with vasculitis.
urticaria
Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction
Urticaria in a horse
vesicle
Fluid-filled elevation of epidermis, <1cm
Vesicles and bullae on ear pinna due to bullous pemphigoid
wheal
Steep-walled, circumscribed elevation in the skin due to edema
Wheals associated with intradermal allergy testing in a horse