This hospital-based observational cross-sectional study aims to investigate the morphometric characteristics of internal organs and the morphofunctional status of the musculoskeletal system in adult patients with previously diagnosed hypothyroidism. The study will evaluate ultrasonographic morphometric characteristics of the liver, pancreas, and kidneys, as well as anthropometric and functional characteristics of the musculoskeletal system. Associations between these outcomes and clinical characteristics, anthropometric parameters, physical activity, and laboratory findings will also be assessed. The study is expected to identify accessible clinical, anthropometric, and functional markers associated with morphometric and musculoskeletal changes in patients with hypothyroidism, thereby improving risk assessment and early detection of systemic involvement.

Hypothyroidism is one of the most common endocrine disorders and is associated with structural and functional alterations affecting multiple organs and body systems. In addition to its metabolic consequences, hypothyroidism may influence the morphology of internal organs and the functional status of the musculoskeletal system. However, comprehensive hospital-based studies evaluating these manifestations simultaneously remain limited.

This observational hospital-based cross-sectional study will include adult patients with a previously established diagnosis of hypothyroidism who are receiving care at participating healthcare institutions. All participants will undergo standardized clinical examination, anthropometric assessment, ultrasonographic evaluation of internal organs, functional assessment of the musculoskeletal system, and laboratory testing according to the study protocol.

Ultrasonographic evaluation will include morphometric assessment of the liver, pancreas, and kidneys using standardized examination protocols. Anthropometric assessment will include body height, body weight, body mass index, waist circumference, hip circumference, calf circumference, arm span, and derived anthropometric indices. Functional assessment of the musculoskeletal system will include handgrip strength, the Five Times Sit-to-Stand Test, and other validated functional assessments specified in the protocol.

The primary outcomes are ultrasonographic morphometric changes of the liver, pancreas, and kidneys, together with morphofunctional impairment of the musculoskeletal system.

Secondary analyses will evaluate associations between these outcomes and demographic characteristics, duration of hypothyroidism, thyroid hormone status, anthropometric indices, physical activity, laboratory findings, and other clinical characteristics.

The findings are expected to improve understanding of systemic manifestations of hypothyroidism and contribute to the identification of practical and inexpensive markers for the early detection of organ involvement and musculoskeletal impairment in routine clinical practice.

Inclusion Criteria:

• Adults aged 18-59 years.
• Previously established diagnosis of hypothyroidism.
• Receiving routine outpatient or inpatient care at participating healthcare institutions.
• Ability to undergo ultrasonographic, anthropometric, and functional assessments.
• Provision of written informed consent.

Exclusion Criteria:

• Pregnancy or lactation.
• History of thyroid malignancy.
• Acute infectious or inflammatory disease at the time of enrollment.
• Severe decompensated cardiovascular, hepatic, or renal disease preventing study procedures.
• Neurological or musculoskeletal disorders that preclude functional testing.
• Refusal or inability to provide informed consent.
• Incomplete clinical or laboratory data.

Adult patients with a previously established diagnosis of hypothyroidism receiving routine medical care at participating healthcare institutions.

The data sharing plan has not yet been finalized and will be determined after study completion in accordance with ethical, institutional, and journal requirements.