Is anti-müllerian hormone useful for monorchidism diagnosis in the tomcat?

Monorchidism is an uncommon condition in tomcats, defined by the congenital absence of one of the testicles. Due to the lack of information regarding possible biomarkers, most monorchidism cases require laparotomy in order to differentiate it from cryptorchidism. Human data suggest that monorchid patients have lower serum anti-Müllerian hormone (AMH) levels when compared to cryptorchids, premises that has been also scrutinized in veterinary medicine. Here, we describe a case of monorchidism in a tomcat, focusing on the clinical findings and the dynamics of AMH serum levels before and after the removal of the singularly identified testicle. To contribute to the limited knowledge of AMH levels across different reproductive statuses in tomcats, the findings from this monorchid case were compared to values obtained from two cryptorchid tomcats (one unilateral and one bilateral), three intact tomcats, and three castrated tomcats. In addition, clinical, histopathological and ultrasound examinations were conducted in all tomcats. The AMH levels in the monorchid tomcat revealed a consistent decrease after surgery, from 27.3 ± 0.2 ng/ml when the testicle was still present, to 2.3 ± 0.2 ng/ml 1 week later, and further decreasing below the detection limit (<0.15 ng/ml) for the last 2 weeks of the trial, matching the AMH level of the castrated male. AMH serum levels of the bilateral and unilateral cryptorchid tomcat (22.5 ± 0.3 ng/ml; 24.1 ± 0.2 ng/ml) were in agreement with those of the three intact males (19.1 ± 2.2 ng/ml) and the monorchid prior to surgery. AMH testing effectively confirmed the absence of testicular tissue after unilateral orchiectomy in a monorchid tomcat but did not differentiate between monorchidism and cryptorchidism. To our knowledge, this is the first case of monorchidism in tomcats, in which AMH levels before and after surgery have been determined.