Why do some dermatophyoses fluoresce with a Wood's Lamp?
tryptophan metabolite that is produced only ON the animal
How does skin act as a sensory organ?
Dermatomes supplied with large sensory nerves that terminate in free nerve endings
& more specialized receptors
What sensations do free nerve endings conduct?
Touch, temperature, pain, pruritus
What are cutaneous receptors for?
Specialized corpuscular receptors - Pacinian and Meissner’s corpuscles Ruffini’s end organs, Merkel’s discs
These are mechanoreceptors (pressure,
vibration) – do they transmit pruritus?
How is pruritus perceived?
Sensation of itch carried centrally from free nerve endings by:
- Non-myelinated, slow conducting C fibers most important (pruritus, pain, heat)
- Myelinated, rapid conducting A delta fibers (noxious stimuli, cold)
How does pruritus reach the brain?
lateral spinothalamic tract
What are the three pain / pruritus theories?
Specificity theory: different subsets of nociceptors transmit pain or pruritus
Pattern theory: spatio-temporal pattern of
neural activity permits distinction
Central processing theory: central processing differences permit distinction between the two sensations
What are the major pharmacological mediators of pruritus?
Histamine, PgE1, leukotrienes (LTB4), opioid peptides, substance P
What is the threshold phenomenon?
What happens IN the animal
A certain pruritic load may be tolerated by an individual without provoking clinical signs, but an increase in that load may push that individual over the threshold initiating clinical signs of pruritus
What does Summation of Effect mean?
What happens TO the animal
Additive pruritic stimuli from different chemical mediators or coexistent skin diseases may raise an animal above its individual pruritic threshold
What are the parts of the hair cycle, and what do they do?
Anagen stage - Mitotically active hair growth phase
Catagen stage - Involutional, no growth
Telogen stage - Long transitional ‘resting’ phase, no active metabolism
Exogen stage - brief phase, telogen hair is shed 'pushed out' by new anagen hair
What major events can affect the hair cycle?
Endocrine disease - Hormonal status
Vascular sustenance - Ischemia of hair follicle
Inflammation - Near hair bulb
Dysplasia - Genetically pre-programmed
How can alopecia be classified?
Traumatic - Common, secondary to pruritus
Non-traumatic - Less common
Congenital - Rare, inherited, permanent
Acquired - Common, many causes
Cicatricial - Follicular destruction & scarring (much more common in humans)
Non-cicatricial - Hair regrowth possible if causative factors can be identified & corrected
What does non-immunological, related to pharmacological action drug reaction look like?
Predictable, dose dependent
Anti-metabolites, other immunomodulators
Alopecia, purpura, poor wound healing, infection
What does a immunological drug reaction look like?
Not predictable, relatively dose independent
Abnormal production of IgE, IgA, IgG, IgM
Immediate, cytotoxic, immune complex or delayed hypersensitivity
What are the clinical features of adverse drug reactions?
can mimic any skin disease
Where are some common places on the body to be affected by an adverse drug reaction?
medial pinna, ventrum, oral cavity, generalized
What is the most common hx of an adverse drug reaction?
Was on a drug previously, stopped, was put back on it in last 2 weeks, developed cutaneous symptoms
What clinical syndromes / diseases are commonly seen with adverse drug reactions?