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1. Introduction and Definitions:

Ulcerative dermatitis is a common and well recognized disease in C57BL/6(B6) mice and related strains. The cause is unknown but is likely multi-factorial with an epigenetic component. Ulcerative dermatitis can lead to alopecia, ulceration, crusting and exudation of the affected areas, and severe pruritus resulting in self-mutilation and deformity. Historically, this condition has responded poorly to a wide variety of treatments and may lead to debilitating lesions if allowed to progress. Recent studies have shown that toenail trims provide lasting and effective treatment (Adams, et al, 2016, ). The us of mice with ulcerative dermatitis for breeding should be limited.

2. Descriptions of Lesions:

• Ulcerative dermatitis may be spontaneous or secondary to a break in the skin. Animals with fight wounds or who have been barbered should be monitored closely for progression to ulcerative dermatitis, especially if on a B6 background.
• Lesions are pruritic and are most commonly located on the dorsal neck, followed by facial, flank and limbs, although lesions may appear anywhere on the body.
• There are no clinical signs that will predict the onset of UD, however, pruritis has been found to correlate with rapid progression due to self-trauma.
• There are 3 common regions for these lesions (see Figure 1 below).
  Region 1 – nose to ears
  Region 2 – ears to mid-abdomen
  Region 3 – mid-abdomen to tail
• Region 1 is considered more severe than regions 2 & 3 due to the increased potential for interference with eating and drinking or involvement of the eye.

3. Treatment Options:

• Trim Nails: Animals should receive a nail trim; cleanse would with chlorhexidine. Monitor mice for up to five days.
• Euthanasia: Animals should be euthanized if the researcher does not require the animal for further research or if the animal exhibits any of the following:
  • Ulceration of the lesions
  • Lesion is >2cm
  • Lesions are located in region 1 and additional regions are also affected
  • Lesions are affecting the eye
• Mice with ulcerative dermatitis must be monitored for additional endpoints outside of those included in the above scoring system. Other endpoint criteria may include:
  • Presence of wounds, scar tissue or contractures that severely impede the animal’s locomotion.
  • Depression, lethargy, loss of body condition and/or anorexia indicating the wounds have resulted in generalized infection.

4. Scoring System:

• The UD scoring system for mice, as described below, utilizes character of the lesion, lesion length and location. This system is useful for groups studying dermatitis or those requiring a mouse to be very closely monitored prior to endpoint euthanasia.
• Mice scored at <75% may undergo treatment; mice scoring ≥75% are considered end-stage of the disease and are to be euthanized.
• Continued Monitoring & Scoring:
  •  Mice undergoing treatment must be monitored and re-scored on a regular basis to ensure that the condition is not worsening during the treatment period (3-5 days).
  • If the score increases, euthanasia is recommended.
  • If the score decreases, monitoring can be continued for an additional 3-5 days.
  • After 10 days, if the mouse has not completely recovered, euthanasia is recommended and/or consultation with a veterinarian.

**length of lesion is determined by measuring the longest diameter of the largest lesion identified. This measurement should involve the lesion only and not cross over clinically normal skin.