Keratoconjunctivitis sicca (KCS), a common progressive inflammatory condition of the cornea and conjunctiva, results from a lack of aqueous tear production. Underlying causes can include congenital alacrima; drug-induced, immune-mediated lacrimal adenitis; irradiation; iatrogenic, systemic disease; or neurologic dysfunction. Any lesion along the parasympathetic nervous system can result in neurogenic KCS, which may be accompanied by Horner syndrome, facial paralysis, or trigeminal nerve deficits, depending on lesion location.

Neurogenic KCS and ipsilateral dry nose were described in 11 dogs with no other neurologic deficits. Suspected causes were idiopathic (n = 9) and trauma (n = 2); most were middle-aged female dogs with no breed predilection. All were treated with oral pilocarpine 1%–2% eye drops (1 drop/10 kg body weight q12h) and topical tear substitutes; topical cyclosporine 0.2% ointment was also used in 5 cases. Oral pilocarpine could be discontinued in 5 dogs (mean, 125 days). An underlying self-limiting process may explain KCS resolution in these cases. Cyclosporine alone may not help with neurogenic KCS. Oral pilocarpine is the choice treatment as a direct-acting parasympathomimetic drug, stimulating the lacrimal glands; this resulted in improved tear production and resolved signs in many cases in this study.

Commentary
KCS can occur as a quantitative or qualitative abnormality of the precorneal tear film. Both types result in progressive inflammation, vascularization, fibrosis, and pigmentation of the cornea and conjunctiva if untreated. KCS with an ipsilateral dry nose is highly suggestive of neurogenic KCS with a lesion affecting the facial nerve and efferent parasympathetic innervation of the lacrimal glands. The majority of neurogenic KCS is idiopathic, but a complete neurologic examination and evaluation for hypothyroidism and diabetes mellitus is indicated. With a lack of parasympathetic innervation, there is an up-regulation of cholinergic muscarinic receptors in the lacrimal glands, resulting in denervation hypersensitivity. This can be used therapeutically by administering a systemic direct-acting parasympathomimetic agent (ie, pilocarpine) in addition to routine lacrimogenic KCS therapy. To avoid atrophy of lacrimal glands, early recognition and prompt initiation of pilocarpine therapy can minimize atrophy secondary to denervation.—David A. Wilkie, DVM, MS, DACVO

Source
Canine neurogenic keratoconjunctivitis sicca: 11 cases (2006-2010). Matheis FL, Walser-Reinhardt L, Spiess BM. VET OPHTHALMOL 15:288-290, 2012.