Pathogenesis

The cause of FOPS is unknown, however, in some cats there may be an association with oral disease. Erupting teeth, dental disease such as periodontal disease, resorptive lesions, and routine dental treatment including tooth extraction, nerve damage during tooth atomization with drills, and mouth ulceration due to infection with Calici virus infection have been associated with some cases².

 In some cats psychological and environmental stressors are thought to be involved². FOPS is likely to be a neuropathic pain disorder, and shows some similarities to trigeminal neuralgia and other orofacial neuropathies in humans. Trigeminal neuralgia in humans in the typical form is characterized by severe acute ‘electric shock like’ paroxysmal pain separated by pain free intervals in specific facial or intraoral areas serviced by the trigeminal nerve³. This may occur either spontaneously, or in response to innocuous tactile stimuli or movement³. Continuous pain may be seen with atypical trigeminal neuralgia.  

 The trigeminal nerve is the fifth cranial nerve and is both motor to the muscles of mastication, and sensory (tactition, thermoception and nociception). Sensory receptors are found throughout the head, face, and roof of the mouth. These transmit information via the afferent fibers of the nerve branches to cell bodies in the trigeminal ganglion. A single large sensory root from the trigeminal ganglion enters the brainstem at the level of the pons4.

 There are several theories on the pathophysiology of trigeminal neuralgia in humans. It is likely that there is an altered threshold for repetitive firing in select neurons, resulting in spontaneous discharges and paroxysms of pain5. Repetitive firing of pathological neurons can spread excitation to neighboring normal neurons, which can change them to produce excessive discharges themselves6. Excessive stimulation may result in central sensitization and possibly the development of continuous pain (as seen in atypical trigeminal neuralgia)5.  Trigeminal neuralgia in humans may be idiopathic, or may be associated with compression of the trigeminal nerve by a nearby blood vessel, cerebellopontine-angle benign masses, or multiple sclerosis3. Another rare orofacial neuropathic pain disorder in humans called glossopharyngeal neuralgia is characterized by sudden recurrent stabbing pains in the distribution of the glossopharyngeal nerve (the back of the tongue, pharynx, middle ear, carotid sinus).  There have been reports of human patients with both trigeminal and glossopharyngeal neuralgia6. As with trigeminal neuralgia, medical management of glossopharyngeal neuralgia can be achieved often by the use of anticonvulsants.  

The current hypothesis on the pathophysiology of FOPS involves damage or disturbance of the sensory endings of the trigeminal nerve resulting in sensitization, combined with a disorder of central processing of trigeminal information². As 92% of these cats are Burmese, this suggests a hereditary predisposition².