P2.26 Spontaneous alopecia and ulcerative dermatitis in C57BL/6J laboratory mice

J.P. Sundberg,¹ Gwendolen Lorch,² Douglas Taylor,³ Kathleen Silva,¹ Jim Miller,¹ Leslie Bechtold,¹ Anthony Nicholson,¹ Ray Vonder Haar,¹ James Fahey,¹ Abigail L. Smith,¹ and Lloyd E. King⁴

¹The Jackson Laboratory, Bar Harbor, ME, USA; ²Ohio State University, Columbus, OH, USA; ³University of Michigan, Ann Arbor, MI, USA; ⁴Vanderbilt University, Nashville, TN, USA

Objectives: C57BL/6J inbred mice and closely related substrains, collectively known as B6 mice, develop transient alopecia and small punctate ulcers that wax and wane, sometimes progressing to severe ulcerative dermatitis. Frequency of disease varies between substrains and is modulated by husbandry practices. Our goal was to define the disease and its progression or healing.

Methods: Histologic, immunohistochemical, and scanning electron microscopic evaluation (with elemental analysis) were done on of groups of 20 mice at weekly intervals for 10 weeks after weaning (at 4 weeks). Wax stripping C3H/HeJ and C57BL/6J dorsal skin was done to resemble controlled barbering.

Results: The first lesion noted was scattered follicular dystrophy affecting only late anagen and early catagen hair follicles. Degradation of the inner root sheath resulted in defects in the cuticle of the hair fiber. Fibers that twisted within follicles sometimes punctured the root sheaths and caused hyperplasia of the root sheaths and foreign body granulomas around free hair fibers in the dermis and hypodermis. Trauma (scratching) induced small ulcers that either healed by pseudoepitheliomatous hyperplasia and dermal scarring or expanded into large, coalescing ulcers with underlying deep beds of granulation tissue. After wax stripping, C3H/HeJ mice had minor epidermal changes followed by rapid and consistent onset of anagen within 7 days. By contrast, B6 skin developed follicular dystrophy and ulcers with marked epidermal hyperplasia.

Conclusions: Inner root sheath changes and foreign body reactions resemble central centrifugal cicatrical alopecia variants (follicular degeneration syndrome, pseudopelade, or folliculitis decalvans). These studies suggest that B6 mice may not be suitable as controls for models for certain skin and hair diseases as they may develop a scarring alopecia similar to human central centrifugal cicatrical alopecia (follicular degeneration syndrome).