Identification of Possible Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a severe neuropathic facial pain condition that is often difficult to recognize early, especially in primary care and dental settings. Many patients initially present with pain that can be mistaken for dental disease or other types of non-dental pain, such as temporomandibular disorders, which may lead to delays in diagnosis and inappropriate dental treatment. A practical screening tool for use in dental practice may support earlier identification and referral of patients with possible TN.

This study will evaluate the diagnostic accuracy of a newly developed questionnaire, the IDentification of possible Trigeminal Neuralgia (IDTN) tool. The IDTN questionnaire was developed with input from patients, dentists, and clinical experts and is designed to capture key features of TN, including pain quality, paroxysmal attacks, pain location, triggers, and related clinical characteristics. This is the first validation study of this tool in a real-world clinical setting. Currently, there is no similar screening tool that has been validated and widely accepted for use in dental practice.

Study Design This is a single-site, prospective, observational diagnostic validation study conducted at University College London Hospitals (UCLH) NHS (National Health System) Foundation Trust, including the Facial Pain Service and Oral Surgery clinics. Adult patients attending for a first appointment with facial or oral pain will be invited to participate. The study is non-interventional and does not alter routine clinical care.

Study Procedures

Participants will complete the 15-item IDTN questionnaire before their specialist consultation, either:

• electronically (via a secure link before attendance, using the electronic health record system), or
• in paper format or via a tablet in the waiting area before the appointment.

The treating specialist will be blinded to the completed questionnaire during the consultation. After the appointment, the research team will record the specialist's final diagnosis from the electronic health record. This will serve as the reference standard for evaluating the questionnaire. If diagnostic uncertainty exists, cases may be reviewed through usual multidisciplinary discussion, and the final clinical diagnosis will be used for analysis.

In addition to questionnaire responses, the study team will collect limited clinical and demographic information from the electronic health record, including age, sex, referrer type, year of first symptoms, and diagnosis. Data will be linked using a study ID and analyzed in anonymized form.

Test-Retest Reliability A subset of participants (20%) will be invited to complete the IDTN questionnaire again within a few days (approximately 2-3 days depending on operational feasibility) to assess the stability of responses over time.

Study Objectives

Primary objective To evaluate the diagnostic accuracy of the IDTN questionnaire for identifying possible TN.

Secondary objectives

• To derive and internally validate a scoring algorithm for the IDTN questionnaire.
• To assess reliability (including test-retest reliability) and validity (including construct/content-related validity) of the tool. To finalize the included items.
• To support future implementation of a practical screening tool in dental and general medical practice.

In the future, the aim is to develop an electronic version of the screening tool with an integrated scoring algorithm, enabling wider use of the tool in the United Kingdom (UK) and internationally.

Outcomes and Analysis Overview

The main diagnostic accuracy measures will include:

• Sensitivity and specificity
• Positive and negative predictive values
• Likelihood ratios
• Receiver operating characteristic (ROC) curve and area under the curve (AUC)

A screening threshold will be selected with priority given to high sensitivity, because the tool is intended to support early identification and referral. A secondary threshold based on the Youden Index may also be reported. A scoring algorithm will be explored using regression-based methods, with internal validation to reduce overfitting. Reliability and dimensionality analyses (including test-retest agreement and factor analysis) will also be performed.

Sample Size The anticipated sample size is 250 participants, with an expected 60 participants diagnosed with TN. An interim analysis will be conducted at 6 months, and if recruitment of new TN cases is lower than anticipated, the study may be expanded to additional facial pain or oral surgery centres using the same methodology to achieve the required numbers. This sample size was calculated to estimate the diagnostic accuracy of the screening tool with 95% confidence intervals and a precision of approximately ±10%, assuming expected sensitivity and specificity of 80%.

Significance If validated, the IDTN questionnaire may provide a practical screening tool to help dental and general medical practitioners identify patients with possible trigeminal neuralgia earlier and refer them more promptly for specialist assessment and treatment. This may reduce diagnostic delay and avoid unnecessary and often irreversible dental procedures.

Inclusion criteria

• Adults aged 18 years or older
• Attending the UCLH Facial Pain Service or Oral Surgery Clinic for their first appointment for facial or oral pain following referral from primary care

Exclusion criteria

• Not experiencing facial or oral pain
• Unable to understand English well enough to complete the questionnaire
• Lacking capacity to provide informed consent
• Insufficient time before their appointment to read the information sheet, provide consent, and complete the questionnaire