Suspect Central Pain When Treatment for Orofacial Neuropathies Fail
LAS VEGAS—Whether called “atypical” facial pain, or “phantom tooth pain,” if edentulous—which Peter Foreman, DDS, consultant, Orofacial Pain, New Zealand, called “useless terms”—clinicians should be alert to pain that may precede or follow dentistry.
The signs and symptoms of oral neuropathies are aching, stabbing, burning, and throbbing, mostly in the upper molar/premolar region. Pain may be intermittent or prolonged, and worse with temperature changes. Hyperesthesia and allodynia may occur.
Neuropathic pain can follow deafferentation, defined as elimination or interruption of sensory nerve transmission due to nerve injury. For example, exodontia, third molar surgery, and endosseous dental implants can all create nerve injuries and neuropathic pain.
“Posterior mandibular implants may result in 5% to 15% of postoperative problems, with permanent neurosensory disorders occurring in approximately 8%,” he said to attendees at PAINWeek 2014. “‘Nerve lateralization' risks perineural damage from ischemic stretching. Implant compression and drill punctures may result in neuroma formation, which can result in permanent pain.”
Orofacial pain occurs more often in females (at a 2:1 ratio to males) and in those primarily older than 40 years of age. Incidence of neuropathy following endodontia ranges from 3% to 6%. Some patients appear to be at risk of whenever endodontia is performed. What remains unknown, however, is whether there is a genetic predisposition. There are few pathological or radiographic signs; for that reason, patients may see many physicians without success.
“Patients with unrelenting pain often visit numerous dentists, dental and medical specialists, and others in search of relief,” Dr. Foreman said. “Many undergo multiple extractions and/or irreversible and often harmful procedures, yet they still have pain.” In fact, he added, many patients continue to suffer but avoid further treatment due to fear of more pain and treatment costs.
He said few dentists and maxillofacial surgeons consult with colleagues such as pain specialists or neurologists. On the contrary, “69.7% rated the efficacy of their procedures highly, despite ongoing problems.” Oral surgeons and endodontists are more likely to see persistent pain patients due to referrals. “Caution is wise if the pain history is long standing. It is a warning that diagnosis and management may prove difficult,” he advised.
Some common responses of dentists to complaints of chronic orofacial pain are summarized in the Table.
Table. Common Dentist Responses to Chronic Orofacial Pain Complaints
| That leaky filling needs replacement
| It must be a "cracked tooth syndrome"
| You need a root canal filling
| I'll have to do an apicectomy
| Let's explore that "bone cavity"
| You've got "TMJ syndrome"
| Your occlusion needs adjustment
| You need a bite splint
| You need an arthrogram
| Sorry I'll have to extract the tooth
| I'll have to refer you to an oral surgeon
In addition, diagnostic and treatment errors are common, which can increase pain and problems. He pointed to one study of 64 patients that found prior to a diagnosis of atypical odontalgia, they collectively visited 16 different specialists, from a dentist to an oncologist to a psychiatrist. In fact, “frustrated clinicians may refer patients to a psychiatrist if no apparent cause for pain can be identified.” Dr. Foreman said statistics show psychiatric morbidity often results from persistent pain; however, “it is seldom the cause. One common dental example is “burning mouth syndrome,” which is often labeled psychogenic. Yet, evidence now shows a neurological etiology is more likely, he said.
A thorough history is essential in diagnosing and managing atypical odontalgia. Patients should be asked about the duration of pain and its cause (eg, caries, injury) and the nature of the pain. For example, deep, dull, aching, intermittent pain of variable intensity suggests myofascial pain, which is often due to muscle overuse, such as bruxism and work habits. Relief is often achieved after the cause is controlled. Conversely, sharp, burning, tingling, or stabbing pain that is constant or intermittent suggests neuropathic pain. Relief is often difficult to achieve and may follow deafferentation, such as extractions, surgery, endodontia, or implants.
“Dental neuropathies are difficult to diagnose and treat,” he said. The “smoking gun” in the process of complex events that lead to the development of central sensitization—and, eventually, atypical odontalgia—may well be prolonged C-fiber activity, he said, because approximately 87% of dental pulp fibers are type C.
Since atypical odontalgia is a central sensitization disorder,invasive procedures that could further exacerbate the situation “should be avoided.” Once central sensitization has developed, pain is likely to continue despite treatment, Dr. Foreman said, adding, “this is a trap for the unwary dentist.” Instead, clinicians should place their emphasis on management.
Preemptive analgesia may be used to try to prevent atypical odontalgia. For example, effective long-acting local anesthesia, supported centrally with perioperative NSAIDs, can help block events that lead to onset of central sensitization as well as development of postoperative rebound pain, reducing analgesic needs. General anesthesia alone will not block C-fiber activity, he pointed out.
Postsurgery, “pain medications should be time contingent, not pain contingent,” he said. “This maintains optimal drug levels and helps prevent breakthrough pain.” Tricyclics such as amitriptyline and nortriptyline are useful. He recommended starting with a low dose (10 mg), increasing gradually for the best effect with minimal side effects. Patients should be warned that such agents are not a cure but can help reduce discomfort. Acetaminophen has a mild effect on central pain if used as an adjunct; however, high dosages should be avoided.
Anti-neuropathic drugs such as clonazepam, gabapentin and pregabalin may provide relief, Dr. Foreman said; however, carbamazepine is seldom prescribed due to significant side effects. Ketamine acts on the NMDA receptor site but also has “major side effects.”
What's important to understand, he said, is that for orofacial pain of nondental origin, “the site of the pain is not always its source. Where the diagnosis is in doubt and the patient is insistent, proceed with caution.”