Etiology

• FOPS has similarities to trigeminal neuralgia in humans and is considered to be a neuropathic pain disorder (ie pain due to abnormal nervous system processing of pain messages).
• Thought to be a dysfunction in the processing of sensory trigeminal information within the brain in combination with damage/sensitization of the ending of the trigeminal nerves, eg by an oral lesion. 

Predisposing factors

General

• Oral lesions - of the tongue, lips or buccal mucosa.
• External environmental factors, eg stress:
  • Stress is often triggered by interactions with other cats, eg in multi-cat households or when other cats invade the territory of an affected cat, but can also occur following visits to the veterinary practice, cattery or cat show.

Specific

• Genetic predisposition.
• Oral lesions:
  • Mouth ulceration.
  • Erupting permanent teeth.
  • Dental disease, most commonly periodontal disease Periodontal disease and dental resorptive lesions Odontoclastic tooth resorption (resorptive lesions).
  • Recent routine dental treatment including extraction Dental extraction.
• Environmental stress:
  • Social variables (territorial invasion of other cats), housing (multi-cat households), and other stress factors (eg visiting a veterinary practice, cattery or cat show).

Pathophysiology

• It is hypothesized that FOPS is an orofacial pain disorder similar to trigeminal neuralgia in people.
• The trigeminal neuraliga is characterized by severe pain in the distribution of the trigeminal nerve, usually the mandibles and/or maxilla. Typically this results in severe, episodic pain often lasting only seconds but then occur relatively frequently over a longer period of time. Mild stimulation (eg touch, facial movement such as eating or drinking and draughts of wind) of the region innervated by the trigeminal nerve can provoke attacks (so-called allodynia). It is often shown to be caused by demyelination of the trigeminal sensory fibers within the nerve root or brainstem, often due to compression by an overlying artery or vein.
• A more unusual human facial pain syndrome, part of the spectrum of trigeminal neuralgia, is glossodynia (burning mouth syndrome). This is described as a burning or prickling sensation of the oral mucosa, most commonly at the front of the tongue. The cause in people is unknown with many cases being termed 'idiopathic'. There been mention of a link with anxiety although it is uncertain if this is more the result of the problem rather than the cause. In many of the affected cats, tongue discomfort seems to be the primary problem and so FOPS may be a feline form of glossodynia.
• It is proposed that affected cats have an underlying, possibly familial, disorder of sensory trigeminal information so that when trigeminal nerve endings are sensitized, eg by dental disease, the consequence is a neuropathic pain disorder.
• Conditions of neuropathic pain can be greatly influenced by many internal and external factors, eg individuals with poor social coping strategies may be more vulnerable.

Timecourse

• Acute onset.
• Clinical signs can be episodic or continuous:
  • Episodic FOPS (80%):
    • Distress often triggered by mouth movement, eg eating or grooming.
    • Episodes lasts between several minutes to several hours.
    • Episodes often preceeding by a short period of behavior suggesting anxiety.
  • Continuous FOPS (20%):
    • Appear to be in discomfort all the time and signs increase in intensity when excited, stressed or following mouth movement.
    • Can severely mutilate oral cavity or face.

Epidemiology

• Predilection to the Burmese cats (all colors) and their crosses suggests a hereditary susceptibility for some cases.