Keratoconjunctivitis sicca attributable to parasympathetic facial nerve dysfunction associated with hypothyroidism in a horse.

The research article discusses a case study of a 6-year-old German Warmblood gelding horse suffering from hypothyroidism, which led to notable facial nerve dysfunction and keratoconjunctivitis sicca. The article underscores the importance of considering hypothyroidism as a potential cause of peripheral neuropathy or keratoconjunctivitis sicca in horses.

Details of the Case

• The horse was brought in for examination due to bilateral blepharospasm (involuntary blinking or spasm of the eyelids) and head shaking. The horse’s eyes were also found to have inflamed and swollen conjunctivas and dull corneas.
• A Schirmer tear test, crucial for diagnosing dry eye conditions, revealed remarkably low values, indicating severe dryness of the eyes.
• The horse’s behavioral manifestations included repetitive head movement, snorting, and the flehmen response, a behavior typically displayed when horses detect certain smells. Upon touch, paresthesia (abnormal sensation) and dysesthesia (unpleasant, abnormal sensation) were noted, with slight muscle thickening around the nose and mouth.
• No other abnormalities were detected upon cranial nerve examination. However, tests showed a low serum thyroxine concentration, a clear indication of hypothyroidism in the horse. Hypothyroidism was thus concluded as the underlying cause for the abnormal nerve function and dry eyes.

Diagnosis and Treatment

• The diagnosing vet attributed the dry eye condition (keratoconjunctivitis sicca) and dry nasal membranes to facial nerve disorder. They also identified a sensory trigeminal nerve disorder, which resulted in the horse’s head shaking and abnormal nose and facial sensations.
• These nerve disorders were classified as peripheral neuropathies likely caused by the horse’s hypothyroid state.
• Therapeutic intervention included topical administration of cyclosporine, sodium hyaluronate, and vitamin A ointment for treating the eyes.
• The horse also started on levothyroxine medication for the hypothyroid condition. Improvements were seen in the horse’s clinical signs and tear production in the following weeks and months. In addition, the levothyroxine treatment brought the horse’s thyroxine concentration back within a healthy range.

Conclusions

• The research emphasizes the need to consider hypothyroidism as a potential diagnosis for horses presenting conditions of peripheral neuropathy or dry eye syndrome (keratoconjunctivitis sicca).
• The case study also affirms the efficacy of levothyroxine treatment in resolving related neurological signs in horses diagnosed with hypothyroidism.