IBM Dietary Surveillance Study

This study will employ an observational, case-control design.

A sample size of 32 participants with inclusion body myositis (IBM) has been determined based on a power calculation designed to detect a strong association (r = ±0.5) between dietary protein practices and various outcome measures related to muscle mass and function. Using a two-tailed test with an alpha level of 0.05 and power of 80% (β = 0.2), the analysis indicated a required sample size of 29 participants. The sample size equation used was appropriate for Pearson's Correlation analysis. To account for an estimated 10% dropout rate, the final target recruitment number is 32. In addition, 15 age- and activity-matched control participants will be recruited. Power calculations for comparisons between IBM and control groups returned lower sample size requirements, reflecting the lower variability typically observed in healthy populations.

Identification of participants with IBM will be carried out at the Tertiary Neuromuscular Service, Salford Royal Hospital (Manchester, UK), and the Neuromuscular Centre (Winsford, Cheshire, UK). Those identified will be approached in clinic or by email with a Participant Information Sheet, the study poster and a Consent to Contact Form. The completed Consent to Contact Form will allow the Manchester Metropolitan (ManMet) research team to follow up with an invitation to a screening visit at the ManMet Institute of Sport (IoS)- a phone call or email. Control participants will be recruited from the local community. If agreed, a phone call will take place to arrange a screening and enrolment visit.

The screening visit to the IoS will last up to 1.5 hours but may end prematurely if the participant is found to be ineligible. During the visit, participants will meet with a researcher who will provide a detailed explanation of the study, including time commitment, risks, and participant rights. Informed consent will then be obtained. Participants will then complete four questionnaires to highlight any contraindications to testing and ensure appropriate matching between the disease and control group. These include: a Demographic and General Health Questionnaire, the sIBM Physical Functioning Assessment, an MRI Safety Checklist and the Physical Activity Scale for Individuals with Physical Disabilities. At the end of this visit, participants will be fitted with two activity monitors secured using medical-grade adhesive (one on the wrist and one on the thigh). They will also be given a paper-based food record or shown the Libro App that will serve as a digital alternative, and a set of questionnaires.

Participants will then complete a four-week home-based monitoring period. During this time, they will wear the activity monitors continuously for seven days to record physical activity, sedentary behaviour, and sleep patterns. They will also complete two 3-day food diaries, spaced three weeks apart, to capture dietary intake (food and drink, excluding water). Additionally, participants will complete a Food Frequency Questionnaire, which asks how often different food items have been consumed over the past year. Throughout this period, participants will also complete the series of validated questionnaires at their own pace. These include a Quality of Life Questionnaire (Short Form-36v2) for overall health and wellbeing, the Nottingham Extended Activities of Daily Living (NEADL) Scale for independence in daily activities, the Modified Fatigue Impact Scale (MFIS), the Visual Analogue Scale (VAS) for pain, the Pittsburgh Sleep Quality Index (PSQI), and the SWAL-QOL questionnaire, which assesses how swallowing impacts quality of life.

After the home-based data collection is complete, participants will return to the IoS for a single laboratory based testing session lasting approximately 3-4 hours. In preparation for this visit, participants will be asked to fast for at least three hours, avoid caffeine for 12 hours, and alcohol for 24 hours. They will also be advised to wear comfortable sports clothing with no or minimal metal components. At the start of the visit, height and weight will be recorded to calculate body mass index. Limb dominance will be ascertained. A small finger-prick blood sample will be taken to measure serum 25(OH)D. Resting metabolism will then be measured using indirect calorimetry. Following this, a whole-body DXA scan will be used to assess body composition, including total and regional fat mass, lean mass, and bone mineral density. This scan will only be undertaken once the participant completes the X-ray Imaging Checklist. Muscle strength and function will be assessed next. Leg strength will be evaluated using an isokinetic dynamometer. Handgrip strength will also be measured using a handheld dynamometer. Finally, participants will undergo an MRI scan lasting approximately 45 minutes. Images will be taken of the thigh and forearm muscles, as well as the head and neck, to assess muscle size, fat infiltration, inflammation, and swallowing function. Standard MRI safety procedures will be followed, including a repeat of the MRI safety checklist prior to scanning.

With respect to the study's primary outcome (relationships between habitual dietary protein intake and total lean mass, as well as muscle strength and physical function measures) correlation analyses will be used to explore the relationships between continuous variables. Depending on data distribution, Pearson's correlation coefficients (parametric) or Spearman's rho (non-parametric) will be used to examine associations between protein intake (g/day, g/kg/day) and a) total lean mass/ fat-free mass (DXA), b) muscle strength (grip strength, knee extensor and flexor torque) and c) Functional capacity (sIFA and NEADL scores).

Multiple linear regression models will be used to assess the predictive value of dietary variables (e.g., protein intake, total energy intake) on muscle-related outcomes (e.g., lean mass, strength, MRI-derived muscle volume). Models will adjust for relevant covariates, including age, sex, body mass index, and physical activity. These models will help establish whether dietary intake independently predicts muscle health beyond demographic and lifestyle factors.

Between-group comparisons for continuous secondary outcomes will use independent samples t-tests or Mann Whitney U tests, as appropriate. ANCOVA will be applied for adjusted group comparisons. For MRI-derived outcomes, two-way mixed ANOVA will examine group × region effects, with post-hoc Bonferroni correction. Friedman tests will be used for repeated non-parametric comparisons where needed. Associations between dietary, metabolic, and functional outcomes will also be explored using correlation and regression techniques, as have been described.

Subgroup analyses will be performed within the IBM group to assess how disease duration, physical activity level, or swallowing severity influence dietary intake, body composition, and function. Stratification may include disease duration (<5 vs. ≥5 years), biological sex (male vs. female) and dysphagia severity (Swal-QOL scores) differences between subgroups will be tested using ANOVA or Kruskal-Wallis tests. Interaction effects may be examined via factorial ANOVA.

This research is sponsored by ManMet University and funded by both the ManMet Faculty of Science and Engineering and Myositis UK.