The purpose of this trial is to investigate whether a therapist-guided Internet-delivered cognitive behaviour therapy (ICBT) programme is feasible for adolescents with body dysmorphic disorder (BDD). The aim is to evaluate feasibility and provide preliminary efficacy data.

Rationale for study: BDD is a prevalent and impairing condition that can be effectively treated with cognitive-behaviour therapy (CBT). However, CBT for BDD is a highly specialised treatment and a majority of adolescents do not have access to it. ICBT can be a way to increase the availability of effective psychological treatments. No study to date has evaluated the feasibility of ICBT for adolescent BDD, but the experience in adults with BDD treated with ICBT is encouraging.

Objectives: To investigate whether a therapist-guided Internet-delivered cognitive behaviour therapy (ICBT) programme is feasible for adolescents with body dysmorphic disorder (BDD). Specifically, the aim is to:(a) establish participant retention, ease of recruitment, acceptability, credibility, and satisfaction, (b) evaluate potential adverse events, and (c) provide preliminary efficacy data.

Trial design and methods: Participants will be recruited nationally and will be offered 12 modules of ICBT for BDD, delivered over a period of 14 weeks. Participants will be assessed before, during, and after treatment, and up to 12 months after the end of the treatment. ICBT non-responders, assessed at post-treatment and one-, two-, and three-months after completing treatment, will be offered CBT delivered via video format (at post-treatment and after the 1MFU and the 2MFU) or traditional face-to-face (F2F) CBT at the OCD and Related Disorders Clinic for Children and Adolescents in Stockholm (after the 3MFU).

The primary outcome is feasibility, as measured by examining rates of participant retention, treatment completion and adherence to treatment content, treatment acceptability, treatment credibility, treatment satisfaction and adverse events during the treatment.

Secondary outcomes include improvement in clinician-reported BDD symptoms, as well as improvement in other clinical measures assessing disorder severity, disorder improvement, self-reported BDD symptoms, depressive symptoms, and functional impairment.

Sample: 20 adolescents and their primary caregivers.

Statistical analysis: Retention, acceptability, credibility, and treatment satisfaction. For retention and acceptability, information on ease of recruitment, number of completed modules, and attrition rates will collected and presented in a descriptive manner. Results from a credibility scale will be summarized in group means and standard deviations. Results from a treatment satisfaction scale will be summarized in group means and standard deviation. Potential adverse events: Type and impact of all potential adverse events will be measured with a specific scale and presented descriptively. Preliminary efficacy: Clinical measures of treatment outcomes will be measured via clinician-reported and self- and parent-reported measures and analysed through linear mixed models to detect within group change over time. Within-group effect sizes will be estimated with Cohen's d. Treatment response: The proportion of treatment responders will be calculated. Treatment response will be defined as a ≥30% reduction on the BDD-YBOCS-A, respective to the baseline score. Further, the investigators will also calculate how many participants are on full or partial symptom remission, defined as a score ⩽16 on the BDD-YBOCS-A.

Inclusion Criteria:

1. Age 12 to 17 years, confirmed by the caregiver and subsequently by the patient record system Take Care.
2. A diagnosis of BDD, based on the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), confirmed by the assessor at the pre-treatment assessment.
3. A total BDD severity score on the BDD-YBOCS-A ≥24. confirmed by the clinician-reported BDD-YBOCS-A performed at the pre-treatment assessment.
4. A minimum of one available caregiver (parent) to support the child/adolescent throughout the treatment. Confirmed by the caregiver at the telephone screening or/and pre-treatment assessment.
5. Regular access to a desktop or laptop computer connected to the Internet, with the ability to receive e-mails, as well as a mobile phone to receive SMS (one of each per family is enough). Confirmed by the caregiver at the telephone screening or/and pre-treatment assessment.

Exclusion Criteria:

1. Previous CBT for BDD for a minimum of eight sessions with a qualified therapist within the 12 months prior to assessment. Confirmed by the caregiver at the telephone screening and/or pre-treatment assessment.
2. Simultaneous psychological treatment for BDD, confirmed by the caregiver at the telephone screening and/or pre-treatment assessment.
3. Initiation, adjustment or change of any selective serotonin reuptake inhibitors (SSRI) within the six weeks prior to the pre-treatment assessment. Confirmed by the caregiver at the telephone screening and/or pre-treatment assessment.
4. A diagnosis of organic brain disorder, intellectual disability or a psychiatric disorder (such as psychosis, bipolar disorder or eating disorder) that could interfere with the completion of the treatment. Confirmed by the caregiver at the telephone screening and/or pre-treatment assessment, with help of information from the caregiver and the child/adolescent, and the MINI-KID interview.
5. Immediate risk to self or others requiring urgent medical attention, such as current risk of suicide or self-injurious behaviours. Confirmed by the assessor at the telephone screening and/or face-to-face or video conference pre-treatment assessment, with help of information from the caregiver and the child/adolescent, and the suicide questions on the MINI-KID interview.
6. Child and caregiver not able to read and communicate in Swedish. Confirmed by the caregiver or assessor at the telephone screening and/or pre-treatment assessment.