Atypical coronary band keratoma as a cause of right forelimb lameness in a Warmblood gelding

A 16-year-old Warmblood gelding had historically been evaluated for a chronic right forelimb lameness, localised with a palmar digital nerve block. The lameness was recurrent despite medication of the right fore distal interphalangeal joint. Magnetic resonance imaging (MRI) showed proliferative intermediate-to-low signal tissue in the location of the dorsal recess of the distal interphalangeal joint, with an overlying defect in the common digital extensor tendon. Given persistent right forelimb lameness over the following 24 months, with no improvement to the medication of the distal interphalangeal joint, a palmar digital neurectomy was performed. Three months following the neurectomy, the patient presented for a grade 4/5 right forelimb lameness. There was a firm, expanding swelling around the coronary band. Repeat diagnostic analgesia showed resolution of the lameness with local infiltration of anaesthetic around the firm swelling. At surgery, a soft tissue mass was surgically resected en bloc. The mass was histologically identified as a keratoma. To the authors' knowledge, there are no published reports of keratoma proximal to the coronary band that does not involve the hoof wall structure or underlying middle phalanx. Surgical removal of the keratoma resulted in significant improvement in right forelimb lameness at the 11-week post-op recheck and resolution of the right forelimb lameness 15 weeks post-operatively.