Difficult diagnosis of facial pain: A case report and mini-review

This case report elucidates pitfalls of clinical and radiologic investigations of neuropathic pain due to trigeminal pathology, and utility of neurophysiologic examination when diagnosing facial pain. Our patient was a 63-year-old woman who developed acute, severe facial pain, first located behind the left eye. Neuralgic exacerbations, paresthesia within lower face on the left and restricted mouth opening occurred during the course of the disease with gradual progression. Brain MRI and CT scans were interpreted as normal at 4 and 10 months after symptom onset. At 9 months, detailed neurophysiologic examination showed severe chronic mandibular neuropathy at the left oval foramen with more prominent disturbance of the thick myelinated nerve fibers than the small fibers suggesting compressive etiology. Guided by the neurophysiologic findings, 11 months after the onset of the symptoms, a new brain MRI with contrast enhancement revealed metastatic adenocarcinoma of the left temporal bone along the mandibular nerve, exactly matching the site indicated by the neurophysiologic examination. Neurophysiologic tests offer cost-effective, sensitive tools for screening and accurate level diagnostics of neuropathy and neuropathic pain, which can be utilized also in the diagnosis of facial pain. In addition, whenever there are progressing neurologic deficits or neurophysiologic signs indicating expansive lesion, despite initially normal findings in the brain imaging studies, repeated MRI examinations are warranted, preferably focusing to the ‘neurophysiologic region of interest’ to avoid radiologic sampling errors. As no isolated technique achieves 100% diagnostic accuracy, only rational combinations of different methods will result in correct diagnosis of facial pain without unnecessary delays. Treatment of neuropathic pain is often delayed because of difficulties in reaching the correct diagnosis. During the work-up, many differential diagnostic alternatives have to be considered, also in patients with chronic orofacial pain. Table 1 shows the most important differential diagnoses of orofacial pain.