Pruritis; Skin Rashes; Rash pathology Flashcards
Causal agent of scabies?
Cercoxi scabii
Inhabit the skin underneath the keratin layer
Arachnid
Nymph stage - 6 legs
Where is itch processed?
Parts of forebrain and hypothalamus
Mediators of itch
> Chemical mediators - histamine, PGE2, ACh, serotonin, kvllikrein, IL2, substance P tryptase.
> Nerve transmission - unmyelinated C fibres (different from pain)
> CNS - opiates, endogenous and exogenous
Which type of antihistamines may help with itch?
sedating as they don’t cross the BBB.
Degranulation of a mast cell
Release of pre formed mediators like tryptase, heparin and histamine
as well as
SYNTHESIS OF NEWLY FORMED MEDIATORS like prostaglandin D2, Leukotrienes C4, d4 and E4
and Platelet activating factor
Causes of itch
PRURITOCEPTIVE: something in skin that triggers itch (dryness, inflammation)
NEUROPATHIC - damage of any sort to central or peripheral nerves causing itch
NEUROGENIC - no evident damage in CNS, but itch caused by e.g. opiate effects on CNS receptors
PSYCHOGENIC - psychological causes with no CNS damage
Psychogenic cause of itch?
Delusions of infestation
Hypochondriacal condition.
Cocaine can cause it
Endogenous opioids can be caused by?
Small bile duct obstruction - Primary Biliary Cirrhosis
Dermographic skin
Stroking skin causes excessive mast cell degranulation and release of histamine and other mediators
Blood vessels become dilated and fluid moves to the surface
What kind of nerves transmit itch?
Unmyelinated C fibres
Xerotic eczema
Direct exposure of itch associated unmyelinated C fibres
causes itch
damaged epidermis/ keratin layer/ barrier function
dry skin
common in elderly and occurs in heated rooms.
Breakfast Lunch and Supper sign
Insect bites/ bed bugs
bites which appear 3 in a row
What kind of itching does lichen plants display?
Pruritoceptive.
Sometimes associated with chronic hep C infection
Itch caused by improper breakdown of compounds in liver.
Prurigo nodularis
Skin disease characterised by pruritic (itchy) nodules
Example of neuropathic itch?
Shingles
herpes zoster virus
Can opiates cause itch?
If so, what type?
Yes. Neurogenic itch.
Conditions that block bile ducts will cause…
Itch
Hepatocellular disease has to be…
itch
Advanced in order for an itch to appear
Does thyroid disease cause itch?
Yes
Does Kidney disease cause itch?
Yes
Carcinoma at head of pancreas obstructing the bile duct can cause…
itch
In Primary Biliary Cirrhosis, does the itch come before or after bilirubin levels rise?
LONG before
? bile salts in skin
Management of itch
> Determine cause (if possible)
> Treat the cause (easiest for pruritoreceptive itch)
> Anti-itch treatments
Anti itch treatments
Sedative antihistamines
Emollients (menthol)
Antidepressants
Phototherapy
Opiate antagonists (ondansetron)
Neuropathic itch - anti epileptics.
Assessment of any rash
Detailed hx
Examination
- distribution/sites affected
- morphology
- secondary features
Commonest form of psoriasis
Chronic plaque psoriasis (psoriasis vulgaris)
Symmetrical Common sites -- extensors - scan, sacrum, hands, feet, trunk - nail
Köbner phenomenon
Psoriasis develops in area of skin trauma
e.g. scratch mark or scar
Auspitz sign
Removal of surface scale reveals tiny bleeding points (dilated capillaries in elongated dermal papillae)
Types of psoriasis
Guttate
Palmoplantar pustular
Erythrodermic
Vulgaris
Comorbidities of psoriasis
Psoriatic arthritis, metabolic syndrome (obesity, hypertension, diabetes, lipid abnormalities)
Crohn’s disease
Cancer
Depression
Uveitis
Pathogenesis of acne
Portal occlusion
Build up of bacteria/ sebum behind portal occlusion
Dermal inflammation
Increased sebum production
Poking spots makes it worse
Distribution of acne vulgaris
Related to sites with most sebaceous glands
Face, upper back, anterior chest
Comedones
Open - blackhead
Closed - whitehead
Features of acne vulgaris
Comedones
Pustules and papules
Cysts
Erythema
Scars atrophic, ice pick, texture changes, hypertrophic
Acne Grading
Mild - scattered papule and pustules, comedones
Moderate - numerous papule, pustules and mild atrophic scarring
Severe - cysts, nodules and significant scarring
What DON’T patients present with in rosacea
No comodones (black heads, white heads)
Rosacea
Nose, chin , cheeks and forehead
Papules, pustules, erythema
NO COMEDONES
Prominent facial flushing exacerbated by sudden change in temperature, alcohol and spicy food
Enlarged unshapely nose - rhinopehyma
Conjunctivitis
Rhinophyma
Rounding of the nose
Enlarged, unshapely nose
Lichenoid eruptions
Damage and infiltration between the epidermis and dermis
Lichen planus
Lichenoid drug eruption
Lichen planus
Violaceous (pin/purple) flat topped shiny papule
Volar wrists, forearms, shins and ankles
Wickham’s striae - fine lace like pattern on surface of papule and buccal mucosa
ITCHY
Bullous pemphigoid
Split is DEEPER through DEJ
Elderly patients
Localised to one area or widespread on trunk/proximal limbs
Large tense bull on normal skin on erythematous base
Blisters burst –> erosions
Non scarring
Itchy eryhtematous plaques may be presenting feature
Nikolsky sign NEGATIVE
Mucosal involvement unlikely
Bullous pemphigus
Split is more SUPERFICIAL, intra-epidermal
Affects scalp, face, axillae, groins
FLACID vesicles , bullae
Lesions rupture to leave raw areas (increased infection)
Nikolsky sign POSITIVE
Mucosal involvement common
HIGH MORTALITY IF UNTREATED
Nikolsky’s sign
Top layers of skin slip away from the lower layers when slightly rubbed
Indicates plane of cleavage within the epidermis
Where are melanocytes found?
Dermal-epidermal junction.
Delayed pressure urticaria
Pressure urticaria is characterised by the appearance of weals after pressure to the skin
