Prosopalgia

Pathophysiological mechanisms and classification of facial pain

Facial pain has two main pathogenetic mechanisms, which frequently coexist in clinical practice:

1. Nociceptive mechanism: pain arises directly from tissue damage in the face followed by the generation of a sustained stream of nociceptive impulses.
2. Neuropathic mechanism: associated with the pathological involvement of nervous system elements. This may involve cranial nerves (trigeminal, glossopharyngeal, intermediate, or facial), cervical root endings (e.g., the occipital nerve), as well as brain structures.

According to the classification of cranial neuropathies, facial pain not associated with dental pathology is divided into several groups:

• Classic trigeminal neuralgia (purely paroxysmal or with concomitant background pain).
• Secondary painful neuropathy (associated with acute herpetic infection, trauma, multiple sclerosis, or tumors).
• Glossopharyngeal neuralgia.
• Burning mouth syndrome.
• Persistent idiopathic (atypical) facial pain.
• Central neuropathic pain (post-stroke or associated with multiple sclerosis).

In most cases, the diagnosis is established clinically. However, neuroimaging (MRI or CT of the head and neck) is indicated for all patients to rule out structural lesions. If no organic pathology is found, a diagnosis of idiopathic facial pain or classic neuralgia is made.

Etiology of trigeminal neuralgia

Trigeminal neuralgia (TN) is the most frequent cause of prosopalgia, leading to patient disability. The condition is slightly more common in women.

• Classic idiopathic neuralgia (85% of cases). The cause is compression of the trigeminal nerve root at its exit zone from the pons. Most commonly, the nerve is compressed by the superior cerebellar artery, and less frequently by a venous vessel.
• Secondary symptomatic neuralgia. Arises due to nerve compression by arteriovenous malformations (AVMs), aneurysms, tumors (acoustic neuroma, meningioma, tuberculoma), or epidermoid cysts. Local processes in the sinuses, pharynx, teeth, and jaws can also serve as triggers.
• Secondary neuralgia associated with multiple sclerosis (1–6%). Develops due to damage to the nerve root myelin sheath or the formation of a sclerotic plaque. Suspicion for multiple sclerosis is raised by young age (under 40 years), bilateral attacks, and persistence of pain between paroxysms.

Pathogenesis: from local injury to central sensitization

The pathogenesis of the disorder is complex and involves both peripheral and central mechanisms:

• Ectopic foci of excitation. Due to local demyelination of the nerve fiber (e.g., from vascular compression), impulses begin to be generated directly along the nerve rather than at the receptors.
• Trigger zones. A specific hallmark of trigeminal neuralgia. Touching specific areas of the face provokes an attack. This is explained by ephaptic transmission—the pathological "crossover" of impulses from thick nerve fibers to pain fibers due to myelin destruction.
• Central sensitization. A continuous stream of impulses alters CNS function. The spinal and sensory nuclei of the trigeminal nerve, thalamus, and somatosensory cortex become hyperexcitable. A stable pain system is formed that responds even to non-painful stimuli.
• Similarity to focal epilepsy. Due to excessive neuronal activity, the pathogenesis of TN is often compared to an epileptic focus.

There is also the bioresonance theory, according to which the vibration of surrounding structures coincides with the natural frequency of the nerve, leading to biological resonance, fiber damage, and altered impulse flow.

Clinical presentation of the paroxysm

The classic pain attack in trigeminal neuralgia has distinct characteristics:

1. Duration and character: the attack lasts from a few seconds to 1–2 minutes, starting and ending abruptly. The pain is unilateral, stabbing, sharp, and described as a burning sensation or an "electric shock." There are always pain-free "remission" intervals between attacks.
2. Localization: predominantly affects the right half of the face. The II and III branches of the trigeminal nerve are most frequently involved, whereas the I (ophthalmic) branch is rarely affected. Early in the disease, pain may be projected locally to a single tooth or gum.
3. Behavior: the patient freezes, fearing movement, and sometimes grips the temple or rubs the cheek.
4. Motor phenomena: severe pain may be accompanied by painful tic (tic douloureux) — reflexive contraction of facial expression or masticatory muscles (e.g., orbicularis oculi).
5. Avoidance behavior: due to fear of triggers (talking, chewing, washing with cold water, shaving), patients stop brushing their teeth, washing their faces, and shaving. Attack frequency varies from occasional to hundreds per day, potentially leading to "status douloureux".

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Features of postherpetic and post-traumatic painful neuropathy.
• Clinical presentation of glossopharyngeal neuralgia.
• Burning mouth syndrome: diagnostic criteria.
• Atypical (persistent idiopathic) facial pain.
• Post-stroke central neuropathic pain.

Other topics in "Chapter 29. Facial Pain"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.