Secondary Trigeminal Neuralgia Caused by Pharyngeal Squamous Cell Carcinoma - A Case Report -
A 49-year-old male visited our pain clinic with the chief complaint of burning pain and sensory loss in the right temporal area and tongue for the previous 2 months. The pain intensity was 10 out of 10 on the numeric rating scale (NRS). The patient had felt a burning sensation on the tongue, as though tasting something hot, for one year before visiting our clinic. During a previous dental clinic visit, the patient had been diagnosed with temporomandibular joint disorder and put on treatment with daily ibuprofen (2,400 mg). Despite this medical treatment, he did not experience symptom relief. Therefore, the patient was transferred to our pain clinic.\nWith regard to medical history, the patient had experienced an episode of herpes zoster at the T4 dermatome 10 months earlier. On physical examination, the patient had neuropathic pain and allodynia in the distribution of the right mandibular nerve (V3). Flexion of the neck and compression of the occipital area induced heavy pain in the patient's head and neck, causing an inability to sleep in the supine position. However, there were no vesicles on his skin and no tenderness in the temporal area. The symptoms corresponded with trigeminal neuritis rather than classical TN. Thus, we first diagnosed the patient as having atypical TN and prescribed carbamazepine (CBZ) 100 mg bid, alprazolam 0.25 mg bid, and nortriptyline 10 mg daily. In addition, enhanced MRI was performed to identify the cause of neuritis.\nAn MRI of the internal auditory canal (IAC) showed a mass in the right parapharyngeal space through the foramen ovale. For further evaluation, an MRI of the paranasal sinus (PNS) with contrast was performed, revealing a 2.3 × 3 × 5.1 cm-sized, ill-defined, heterogeneously enhancing mass in the right parapharyngeal space and the right masticator space (). We had a high suspicion that the mass was a neurogenic tumor. The whole-body fluorodeoxyglucose (FDG) fusion PET showed suggestive of malignancy in the right parapharyngeal space and the right masticator space, while other areas showed no abnormal FDG uptake suggesting malignancy (). For the relief of TN, a right V3 root block via an infrazygomatic approach was performed in our pain clinic (), and then an otolaryngologist performed an endoscopic transpterygoid biopsy for pathologic evaluation.\nCBZ was very effective in treating the patient's TN, as the NRS value decreased from 10 to 3. However, a skin rash on the entire body developed suddenly 20 days later, which was thought to have been induced by CBZ. Thus, we stopped CBZ and started the patient on gabapentin 300 mg tid and oxycodone 5 mg tid. After 3 days, the skin rash disappeared, and the pain was well-controlled, with the NRS value maintained at 1 or 2. The patient was scheduled for radiation and chemotherapy.