Facial Pain: Diagnostic Considerations and Role of Neuroimaging

Facial pain is one the challenging issues in medicine which has wide differential diagnosis. Therefore, a wide range of specialties including neurologist, otolaryngologist, pain medicine anesthesiologist, dentist and neurosurgeon can be involved in patients’ diagnosis and management.Except cases with classical trigeminal neuralgia, which vascular compression is evident in MRI and cases of secondary trigeminal neuralgia due to multiple sclerosis or space occupying lesion, in rest of the cases with facial pain, imaging studies seems to be less diagnostic.Similar to most of headache syndromes, facial pain is a purely subjective with no obvious objective signs, therefore the diagnosis very much relies on the descriptive characteristics of the pain. A thorough history and physical should be given to every patient complaining of facial pain. The pain history needs to include key components in order to come up with a specific differential diagnosis:• Timing of the pain needs to be determined including when the pain started, how long the pain lasts, and how often the patient experiences the pain.• Location and radiation can be strong determinants of the source of pain. As such, an expert knowledge of dermatomes and nerve distribution is crucial.• Quality of pain is usually documented with modifiers such as throbbing, stabbing, dull, or sharp. The presence of sudden, paroxysmal intense, jabbing and lancinating pain, lasting from only a few seconds to less than 2 minutes with period of refractory phases, is characteristic for neuralgia .• Severity can be assessed using pain scales, such as the visual analogue scale (VAS). The VAS ranges from 1 to 10, with 1 being minimal pain and 10 being the worst pain imaginable. This is the most subjective component of history and therefore has less importance.• Relieving and aggravating factors of the pain. For example trigeminal neuralgia almost invariably trigger by touching and cold wind. On the other hand chewing or brushing teeth can trigger trigeminal neuralgia but also can aggravate facial pain due to dental pathology and therefore it has less specificity.• Medical, family, and social history while ruling out any history of dental disease, orofacial disease, or surgery prior to the initial onset of symptoms.Facial pain can be the presenting, and sometimes the only, complaint of many disorders that originate from cranial structures. In the clinical setting, the identification of the underlying cause, and therefore the decision about the investigations needed, occasionally represents a challenge, even for experienced physicians.Although Trigeminal Neuralgia is the most well-known etiology of facial pain and in practice majority of patients with facial pain label as trigeminal neuralgia, but in real world minority of patients with facial pain, has classical trigeminal neuralgia.Differential diagnosis of facial pain beside trigeminal neuralgia includes:A. Central demyelinating disorder (Multiple sclerosis)B.Autoimmune neuropathy: SLE, Sjögren s syndrome, progressive sclerosis /scleroderma, Rheumatoid arthritis, other connective tissue disease including MCTD /UDCTC. Infection: Herpes zoster (post-herpetic neuralgia), Herpes simples, Syphilis, Leprosy D. Space-occupying lesions (tumors): Intracranial, Gasserian’s ganglion, trigeminal branches, OdontomasE. Trauma: Dental avulsion (lower third molar) , Implamtology, Endodontic treatment,F. Toxic agents: stilbamidine*, trichloroethyleneG. Other: Sarcoidosis, Amyloidosis, Vascular (vertebra-basilar) disease Among the above differentials, autoimmune disorder is less discussed in literatures, particularly in neurology. Therefore there is high likelihood that lots of patients who have autoimmune trigeminal neuropathy, label as trigeminal neuralgia and it is not uncommon that those patient go under unnecessary, often invasive, procedure including microvascular decompression.Rheumatologic etiology of facial pain has been less discussed and recognized. These are the patients who usually classified as persistent idiopathic facial pain (PIFP) by international classification of headache disorder (ICHD-3) or label as atypical face pain. Majority of them do not get relief from routine therapeutic modalities and some of them end up being on chronic opioid which facilitate the development of anesthesia dolorosa. Neurologic manifestation of autoimmune disorders, including Sjögren Syndrome (SS) is well known but less described in literatures. Most studies on neurological involvements of autoimmune disorders focused on peripheral nervous system, mainly painful sensory neuropathy. It seems central nervous system and cranial nerve, particularly trigeminal nerve involvement, which can present with face pain, has been underestimated and under-looked. Painful trigeminal neuropathy secondary to autoimmune disorders always needs to be in consideration as the differential diagnosis of face pain, specifically in :A. Age of under the 50 years and specifically < 40 years old when facial pain startedB. Concomitant sensory symptoms with their facial painC. Persistent face painD. Presence of other rheumatologic symptoms, e.g, xerostomia or sicca syndrome, unexplained arthritis, skin rash.In those patient complete autoimmune panel needs to be send. In more suspicious cases other diagnostic methods, including minor salivary gland biopsy, dedicated MRI or CT scan of the face or even biopsy of other peripheral nerve might be helpful to make the diagnosis.