Unilateral idiopathic sensory trigeminal nerve paralysis in a dog

ABSTRACT

Background: A spayed-female mixed breed dog was presented due to 2 years reduced visual acuity in the left eye. The investigation revealed corneal melanosis, keratoconjunctivis sicca and loss of facial sensation in the same side. The aim of this report is to describe an unilateral idiopathic sensory trigeminal nerve paralysis and keratitis as consequence of corneal innervation loss was established. Unilateral sensory trigeminal nerve paralysis is a very rare lesion in dogs and causes are unclear. Case A 5-year-old spayed-female mixed breed dog was presented with a history of two years reduced visual acuity in the left eye. The Schirmer tear test values (without use of topical anesthetic) were 11 and 17 mm/min in the left and right eye respectively. Fluorescein tests were negative for both eyes. All postural reactions and spinal reflexes were normal. Cranial nerve evaluation identified symmetrical facial muscles (temporalis, masseter), indicating no muscle atrophy and normal motor nucleus of the fifth nerve. Absent sensation at the upper and lower lips margins, cornea, eyelids (medial and lateral canthi) and sensation in left nasal side were noted. No palpebral reflex was noticed, but there was spontaneous blinking of eyelids, which indicated normal facial nerve function. All other cranial nerve reflexes including menace response, oculocephalic, and gag reflexes were normal. The owner declined further workup, including cerebrospinal fluid analysis and images studies. According to the clinical presentation and neurological findings, presumptive diagnosis of unilateral idiopathic sensory trigeminal nerve paralysis was established. The dog was observed over 18 months without any clinical improvement. The Schirmer tear test showed same values (12 mm/min) and the melanosis remained unchanged.Discussion: Lesions that affected trigeminal nerve, trigeminal ganglion, or trigeminal tract in the pons and medulla caused facial hypoalgesia or analgesia...