Trigeminal neuralgia (TN) is a severe type of non-dental orofacial pain that can feel like sudden electric shocks in the face and is often mistaken for tooth pain or other dental problems. This can lead to delays in referral and unnecessary, sometimes irreversible, dental treatment. The goal of this observational study is to evaluate how well a new questionnaire (IDentification of possible Trigeminal Neuralgia - IDTN) identifies adults with possible trigeminal neuralgia among patients attending hospital clinics with orofacial pain, with the aim of supporting its use in dental and general medical practice to improve early recognition and referral.

The main questions it aims to answer are:

• How accurately does the IDTN questionnaire identify patients with possible trigeminal neuralgia compared with the specialist clinical diagnosis?
• Which combination of questionnaire items best supports a practical screening score for use in dental and/or general medical practice?

Participants will:

1. Complete the IDTN questionnaire before their clinical appointment (either electronically or on paper)
2. Undergo their usual specialist clinical assessment, during which the final diagnosis will be recorded
3. Allow the research team to compare questionnaire responses with the specialist diagnosis (the reference standard)

A subset of participants will also be asked to complete the questionnaire again a few days later to assess test-retest reliability.

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

Participants will be recruited from two clinical settings at University College London Hospitals (UCLH): the Facial Pain Service and the Oral Surgery Clinic. Eligible participants will be identified using clinic codes that indicate first-time attendance for pain-related referrals from primary care. This population includes individuals referred from primary care because of facial pain, dental pain, or suspected orofacial pain conditions, including trigeminal neuralgia.

Fully anonymized individual participant data (IPD) that underlie the published results will be shared. This will include anonymized responses to the IDTN questionnaire, demographic variables (such as age and gender), and the final clinical diagnosis used as the reference standard. All direct identifiers will be removed, and data will be de-identified according to UCL/UCLH (University College London/University College London Hospitals) data governance requirements before sharing.

Anonymized IPD and supporting materials will be available 6 months after publication of the main study results and will remain available for up to 5 years thereafter.

Access will be provided to qualified researchers for scientifically justified purposes. Requests must be submitted in writing to the Chief Investigator and will be reviewed jointly by the research team and sponsor (UCL). Approved researchers will sign a data sharing agreement and will receive access to anonymized datasets through a secure transfer mechanism.