Changes in tear production in a dog with keratoconjunctivitis sicca for a year after inevitable nictitating membrane gland resection due to suspicion of a malignant tumour.

Since the removal of the NM causes KCS in dogs, it was contraindicated to remove the NM unless unavoidable such as in a malignant tumour. However, to the best of author's knowledge, there are no reports of conjunctivitis and keratitis owing to decreased tear production following removal of the NM gland. This case study demonstrates the tear production changes in a dog for a year after removal of the nictitating membrane (NM) due to suspicion of a malignant tumour. A 13-year-old spayed female English Cocker Spaniel who had suffered from severe ocular discharge, discomfort, keratoconjunctivitis sicca (KCS), and NM enlargement in the right eye was brought to our hospital. The dog could not tolerate treatment with topical 0.2% cyclosporine or corticosteroids. The dog's right eye had NM gland prolapse, severe follicular conjunctivitis and a very low Schirmer tear test-1 (STT-1) value of 3 mm/min. Furthermore, the result of fine needle aspiration of the enlarged NM gland suggested a risk of malignancy. Despite the risk of KCS, complete NM resection was performed to diagnose the tumour. Fortunately, the final histopathological evaluation revealed chronic inflammation without any evidence of malignancy. Contrary to concerns that the STT-1 value would further decrease after the removal of the NM gland, the STT-1 value remained elevated compared to that before surgery, and the clinical symptoms improved for a year. It is generally known that NM gland resection is not recommended due to the risk of developing iatrogenic KCS unless a malignant tumour is suspected. In this case, surgical removal of the inflammatory NM gland that was not responsive to medications had a positive effect on KCS. Since the inflammatory and structural disease of the NM was strengthening KCS, the outcome was thought to be different from that when the normal third eyelid was removed.