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13. The Skin > 13.2 Itching Skin > Flashcards

13.2 Itching Skin Flashcards

1
Q

Define itch

A
  • Sensation (usually unpleasant) that elicits a desire to scratch
  • Important protective mechanism that allows an animal to detect harmful substances
  • Resultant scratching behavior, can sometimes induce a pleasant feeling, leading to an itch-scratch cycle.
  • This itch-scratch cycle can result in serious skin damage and propagates the itch
  • Pruritus is the most common complaint of patients with dermatologic disease
  • Often arises from a primary skin disorder
  • Represents a manifestation of an underlying systemic disease in approximately 10% to 25% of affected individuals
  • In some patients, pruritus occurs in the absence of visible skin signs
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2
Q

Itch scratch cycle

A
  1. Itch
  2. Automatic Scratch
  3. Epidermal barrier / skin damage
  4. Neuropeptides, tryptase
  5. C nerves fibres
  6. More itching
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3
Q

Classification of itching

A

Mechanical
- physical stimulus

Chemical itch
- histamine-dependent
- histamine-independent

‘contagious itch’
- Watching others scratching themselves or even talking about itchiness can induce a desire to scratch in humans, despite no chemical or mechanical pruritic input

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4
Q

Itch pathway

A

Complex:
- Itch signal transmitted mainly through small, itch-selective C-fibres, histamine and non-histamine triggered neurons
- Connect with secondary neurons in dorsal root ganglion
- Cross to opposite side of the spinothalamic tract
- Ascend to parts of the brain involved in sensation, emotion, reward and memory.

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5
Q

Itching mediators

A
  • histamines
  • tryptase
  • cathepsin S
  • interleukin-31
  • prostaglandins
  • opioid receptor agonists
  • interleukin 2
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6
Q

Causes of itch
With skin rash
No skin rash

A

With skin rash
- Skin disease with primary skin changes:
• Atopic eczema
• Psoriasis
• Fungalinfection
• Papularurticaria
• Insectbites
• Scabies
• Etc
- Secondary skin changes – changes due to scratching (itch-scratch cycle triggering local small fibre neuropathy)
• lichen simplex chronicus

No skin rash
- Systemic disease
- Underlying malignancy (paraneoplastic)
- Medication
- Advanced aging
- Neurogenic/neuropathic itch

Primary skin diseases: Slide 11

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7
Q

Atopic dermatitis / eczema: Atopic Dermatitis
General
Pathogenesis

A

Atopic Dermatitis
- chronically relapsing,
- inflammatory,
- non-contagious and
- extremely pruritic skin disease occurring
- often in families with atopic diseases.
*Atopic diseases - group of diseases that gets inherited together (asthma, allergic conjunctivitis, food allergies, etc)

Pathogenesis
- complex genetic disease that arises from gene-gene and gene-environment interactions
- Slide 15
- Barrier dysfuction
↕️ Type 2 inflam contributes to skin barrier dysfunc in AD
- Th2 inflammation

Slide 17-22

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8
Q

NB! T-helper 2 pathway of AD

A

Dendrocytes (antigen presenting cells)
⬇️ stim production
IL-4
⬇️ stim
Th 2 cells / lymphocytes
⬇️ produce
IL-4 & IL-13
⬇️ triggering
Type 2 inflammation
⬇️
Keeps process going

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9
Q

Define psoriasis

A
  • a complex, chronic, multifactorial, immune-mediated, inflammatory disease characterised by clearly defined, red and scaly plaques
  • normal skin in between plaque
  • Hyperproliferation of the keratinocytes in the epidermis, with an increase in the epidermal cell turnover rate
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10
Q

Pathogenesis of psoriasis

A
  • complex
    Multifactorial
  • Genetic (certain HLA-alleles)
  • Environmental:
    • Stress
    • Cold, trauma,
    • Infections (eg, streptococcal, staphylococcal, human immunodeficiency virus),
    • Alcohol, and drugs (eg, iodides, steroid withdrawal, aspirin, lithium, beta-blockers, botulinum A, antimalarials)
    Immunologic:
    Inflam pathway
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11
Q

Inflam pathway involved in psoriasis

A

Dendrocytes (antigen presenting cells)
⬇️ stim production
IL-23
⬇️ stim
Th 17 cells / lymphocytes
⬇️ produce
IL-17A
⬇️stim
Keratinocytes to hyperproliferate
⬇️ triggering
Neutrophils + hyperinflam response
⬇️
Keeps process going

Th 1 disease

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12
Q

Classify fungal skin infec

A
  1. Dermatophytes
  2. Non-dermatophytes:
    - Yeast-like fungus - Candida albicans
    - Molds - eg: Maalassezia furfur
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13
Q

What will you see under a microscope with Potassium Hydroxide (KOH), what will you see in:
Dermatophyte
Candida
Malassezia

A

Dermatophyte
- septate hyphae

Candida
- round or oval cells
- Pseudohyphae
- septate hyphae (sometimes)

Malassezia
- Yeasts and hyphae – typical ‘spaghetti and meatballs’

Terms used for dermatophyte infec:
- ringworm
- tinea

  • only grow in keratin (stratum corneum, hair, nail)
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14
Q

List 3 dermatophyte infections

A
  • Microsporum➡️canis
  • Trichophyton➡️violaceum
  • Epidermophyton➡️floccosum
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15
Q

Types of dermatophytes based on mode of transmission

A

Anthrophilic
- human to human
- most common

Zoophilic
- Animal to human

Geophilic
- Soil to human or animal

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16
Q

Papular urticaria

A
  • Very common - children
  • Hypersensitivity response to antigens in arthropods’ saliva
  • Immunological tolerance develops - less common in adults
  • Arthropods
    • Fleas (Dogs, cats; BIRDS – check if nesting in roof!)
    • Bed bugs
    • Mosquitoes
    • Mites
  • Often recurs when exposed to new insects at new venues
17
Q

Insect bites

A
  • Lice
    • Pediculosis: Head lice (Pediculus capitis)
    • Clothing lice (Pediculus humanus)
    • Crab lice (Pthirus pubis)
  • Fleas
  • Bed bugs (Cimex lectularius)
  • Animal mites
  • Ticks
    May be vectors for serious infections
18
Q

General itch: Systemic diseases associated with pruritus

A
  • uremia
  • obstructive liver & biliary disease
  • hemotologic disease
  • lymphoreticular disease
  • malignancy
  • endocrinological diseases
  • neurological disease
  • infectious disease
  • rheumatic disease
19
Q

NB Paraneoplastic pruritus

A
  • May precede, follow or occur concurrently
  • Generally improves when malignancy cleared
  • Often recurs during remission
  • Skin appears normal, except for secondary changes (e.g. excoriations)
  • Mechanism: not fully understood
  • Any malignancies BUT commonest:
    • Haematological malignancies (leukemia and lymphoma)
    • Cholangiocarcinoma
  • Alot of medications can trigger (TB, cocane, morphine)
20
Q

Advanced age - dry skin

A
  • Inherited factors contribute
  • Increasing age, resulting in decreased production of ceramides in stratum corneum.
  • Mostly legs, but can become widespread
  • Cool weather, especially when windy or the humidity is low.
  • Air conditioning, central heating or sitting close to a fire or fan heater.
  • Excessive bathing, showering or swimming, especially in strongly chlorinated hot or cold water.
  • Contact with soap, detergents and solvents.

13. The Skin (9 decks)

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