Nail lesions in 30 old inbred mouse strains

Abstract

In a large scale aging study, 30 inbred strains were necropsied at 12, 20, and greater than 20 months of age. Ten strains were identified with nail lesions; the highest frequency was noted in NON/ShiLtJ mice. To determine if these lesions occurred in younger mice, NON/ShiLtJ mice, 57-241 days of age, were obtained. Lesions identified fell into two main categories: acute to chronic penetration of the third phalangeal bone through the hyponychium with associated inflammation and bone remodeling or metaplasia of the nail matrix and nail bed associated with severe orthokeratotic hyperkeratosis replacing the nail plate. Penetration of the distal phalanx through the hyponychium appeared to be the initiating feature. The acute to subacute inflammatory response was associated with osteolysis of the distal phalanx. The highest frequency of nail lesions was in the NON/ShiLtJ and NZW/Lac1J strains with a strong female predilection. Younger NON/ShiLtJ mice revealed that these lesions were infrequent or affected only one digit. The only other nail unit abnormality identified was sporadic subungual intraosseous epidermoid inclusion cysts that closely resembled similar lesions reported in humans, dogs, and horses.