ITCH

1
ITCH

• Allison Covey, Sara Haug, Lindsey Oehlerking,
  Megan Saunders

2

• Your roommate Laura complains constantly of an
  itch that began shortly after she moved into your
  dorm room. She explains that she has a lot of
  allergies, and that its probably just another
  allergic reaction to something in the room.
  Youre not very sympathetic. You dont think her
  rash looks that bad (Ive had worse), but it
  has caused her to lose sleep, and her scratching
  has irritated her skin further. You decide to
  research itch in order to become more empathetic.
  
• Describe the pathogenesis of itch, including
  possible paracrine messages that mediate the
  sensation, the nervous pathway that carries the
  information for perception, and a possible
  therapy aimed at controlling her hyperactive
  immune system.

3
Pathogenesis of Itch (Pruritus)

• Lauras hyperactive immune system responds to an
  antigen, although it is not dangerous

Causes production of Immunoglobulin (IgE - a type
of antibody)
Antigens bind to IgE, stimulating the release of
histamine, cytokines, and leukotrienes
IgE binds to mast cells and basophils
4
Nervous Pathway

• Histamine binds to H1 (a histamine receptor) on a
  non-myelinated (slow-conducting) C-fiber which is
  a primary nociceptive neuron at the
  epidermal/dermal junction

This closes K channels that would normally be
open when the neuron is resting
Histamine also prevents hyperpolarization after
the action potential, thus shortening the
relative refractory period
Cell depolarizes and produces an action potential
5
Nervous Pathway, contd

• Conducted to cell body in dorsal root ganglion
  via afferent nerve

I have an itch
Synapses at secondary neuron in the spinal cord
Action potential goes to thalamus
Sent to post-central gyrus of the cortex
6
Nervous pathway, contd

• Signal sent to pre-central gyrus that initiates
  the need to scratch.

Recruits effector to induce scratching.
7

• Why do we have to scratch?
• The scratch response originally evolved as a
  mechanism to remove irritant. Scratching may also
  physically interrupt transduction of the itch.

The itch-scratch-itch effect Scratching an itch
helps alleviate the itch but it also damages mast
cells. The damaged mast cells release histamine
which initiates the itch sensation all over
again.
8
Treatment

• Cause-specific
• Wear cool clothes
• Avoid heat
• Keep nails short and rub the itch instead of
  scratching
• Switch to milder soaps and lotions that dont
  have perfumes and dyes in them
• Antihistamines (H1 receptor antagonists)
• Topical corticosteroids which inhibit the
  production of cytokines and chemokines, thus
  decreasing inflammation and cellular recruitment
• Antibiotics for secondary infections from
  scratching
• UV-B light for severe cases to kill mast cells to
  prevent release of histamine (too serious for
  Laura!)

9
Urkel saves the daynot really
Did I do that?

• Steve is a hyperactive immune system. He thinks
  he needs to protect Laura, but he just makes
  everything worse.

10
References

• Silverthorn, D.U. Human Physiology. 4th edition.
• Peharda, V., et al. Pruritus an Important
  Symptom of Internal Disease. ACTA. 2000 vol 9
  No. 3
• http//www.clevelandclinicmeded.com/diseasem anage
  ment/dermatology/pruritus.htm
• Twycross, R. et al. Itch scratching more than
  the surface. http//qjmed.oxfordjournals.org/cgi/c
  ontent/full/96/1/7
• http//www.worldallergy.org/professional/allergic_
  diseases_center/ige/