This prospective observational study aims to evaluate the validity of ultrasonographic muscle measurements in patients with inflammatory bowel disease (IBD). Sarcopenia is commonly assessed using computed tomography (CT)-based skeletal muscle area measurements at the L3 vertebral level, which are considered a gold standard method. However, CT is not always feasible due to radiation exposure and accessibility limitations.

In this study, muscle strength will be assessed using handgrip dynamometry, and muscle mass will be evaluated using ultrasonography of selected skeletal muscles. In patients with available recent abdominal CT imaging, L3 skeletal muscle area will be recorded. The primary objective is to compare ultrasonographic muscle measurements with CT-based assessments and to evaluate the agreement between these methods.

This study aims to determine whether ultrasonography can serve as a practical and reliable alternative tool for muscle mass evaluation in patients with IBD.

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is associated with an increased risk of sarcopenia due to chronic systemic inflammation, malnutrition, and treatment-related factors. Accurate assessment of muscle mass is therefore clinically relevant in this population.

Computed tomography (CT)-based skeletal muscle area measurement at the L3 vertebral level is widely accepted as a gold standard for muscle mass assessment. However, CT involves radiation exposure and is not always readily available for repeated evaluation. Ultrasonography (USG) has recently emerged as a promising, non-invasive, radiation-free, and easily accessible method for muscle evaluation, but its validity in patients with IBD requires further investigation.

This single-center, prospective, observational study will enroll adult patients (≥18 years) with a confirmed diagnosis of IBD. Muscle strength will be assessed using handgrip dynamometry. Ultrasonographic measurements will be performed to evaluate thickness and cross-sectional area of selected skeletal muscles, including rectus femoris, vastus intermedius, gastrocnemius medialis, biceps brachii, rectus abdominis, and internal oblique muscles.

For patients with available abdominal CT imaging within the previous six months, skeletal muscle cross-sectional area at the L3 vertebral level will be measured from archived images. The primary outcome of the study is the correlation and agreement between ultrasonographic measurements and CT-based L3 muscle area. Secondary analyses will evaluate associations between muscle measurements, clinical characteristics, and laboratory parameters.

No additional invasive procedures or laboratory tests will be performed for research purposes.

Inclusion Criteria:

• Age ≥18 years
• Established diagnosis of inflammatory bowel disease (ICD-10: K50.* Crohn's disease, K51.* ulcerative colitis)
• Ability to provide written informed consent
• Ability to undergo ultrasonographic muscle assessment and handgrip strength testing
• Availability of an abdominal computed tomography (CT) scan performed within the previous 6 months

Exclusion Criteria:

• Known neuromuscular disorders or primary muscle diseases
• Major orthopedic conditions affecting muscle strength assessment
• Pregnancy
• Abdominal wall defects or conditions interfering with ultrasound assessment
• Incomplete clinical or imaging data
• Any condition preventing reliable ultrasound or handgrip measurement

Adult patients with inflammatory bowel disease (Crohn's disease or ulcerative colitis) followed at a tertiary care center and undergoing muscle mass and strength evaluation.

Individual participant data (IPD) that underlie the results reported in this study (after de-identification), including demographic data, laboratory parameters, and outcome measures, will be made available beginning 6 months after publication and ending 5 years after publication.

Data will be shared with researchers who provide a methodologically sound proposal and sign a data access agreement.

Requests should be directed to the corresponding author. The study protocol and statistical analysis plan will also be made available upon reasonable request.

De-identified individual participant data underlying the results reported in this study will be available beginning 6 months after publication of the primary results and ending 5 years after publication.

Data will be made available to researchers who provide a methodologically sound proposal. Proposals will be reviewed by the study investigators. Data access will be granted upon approval and signing of a data use agreement. Only de-identified data will be shared. Requests should be directed to the corresponding author.