Pathogenesis of canine interdigital palmar and plantar comedones and follicular cysts, and their response to laser surgery

This study documents the presence of comedones and follicular cysts of palmar and plantar interdigital skin as an underlying cause of recurrent dermatitis, and describes the use of a carbon dioxide laser to surgically remove lesions. The 28 dogs included in the study had: (i) recurrent lameness, pain, and nodules, or draining sinuses in the dorsal interdigital skin, (ii) failed to respond to antibiotic therapy, and (iii) were negative for Demodex mites and dermatophytes. All 28 had laser surgery; nine dogs had two surgical procedures and two dogs had three surgical procedures for lesion recurrence. Fifteen dogs had skin samples collected for histopathology. Clinical features in ventral interdigital skin included alopecia, callus-like thickening, and comedones. Histological features included hyperkeratosis, acanthosis, comedones and follicular cysts, furunculosis, draining sinuses, and scarring. Surface trauma to the ventral interdigital skin appeared to contribute to lesion development. Laser surgery allowed removal of multiple layers of cysts and adjacent hair follicles and the tracking and removal of sinuses. One dog was euthanized for orthopaedic lameness 1 month after laser surgery, but post-surgical follow-up (1.0-8.0 years - mean 3 years) from the remaining 27 dogs revealed that laser therapy of affected skin and adjacent hair follicles resulted in resolution of interdigital lesions in 25. Two dogs continued to develop interdigital cysts.