Lipedema is a chronic disorder characterized by abnormal bilateral fat deposition in the extremities, predominantly affecting women and typically beginning at puberty. The trunk, hands, and feet are usually spared. Despite its relatively high prevalence, lipedema is frequently underrecognized in clinical practice and is often confused with conditions such as obesity, venous insufficiency, and lymphedema. Patients commonly present with pain, tenderness, and easy bruising.

Current imaging methods have demonstrated increased subcutaneous tissue thickness and fluid infiltration in lipedema; however, no imaging modality has yet been established as a definitive diagnostic tool. Shear wave elastography (SWE) is a noninvasive ultrasound-based technique that enables quantitative assessment of tissue stiffness and may provide additional information regarding tissue structure and mechanical properties.

In this study, we aim to compare lower extremity subcutaneous tissue stiffness in patients with lipedema and healthy controls using SWE. As a secondary objective, we aim to evaluate abdominal subcutaneous tissue stiffness in patients with lipedema and compare these findings with both lower extremity measurements in the same patients and abdominal measurements in individuals without lipedema.

Lipedema is a disorder characterized by abnormal bilateral fat deposition in the upper and lower extremities, typically beginning at puberty and predominantly affecting women. Its prevalence in the female population is estimated to be approximately 11%. The condition primarily involves the extremities, while the trunk, hands, and dorsum of the feet are typically spared. It has a genetic predisposition and is influenced by hormonal factors. Despite being relatively common, lipedema is frequently overlooked in daily clinical practice. Therefore, accurate clinical recognition of the disease is essential. In the differential diagnosis, it is often confused with obesity, venous insufficiency, and lymphedema. The main symptoms reported by patients with lipedema include pain, tenderness, and easy bruising.

Previous imaging studies using Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) have demonstrated thickening of the subcutaneous tissue without muscle edema, along with fluid infiltration within adipose tissue.

Ultrasonography (US) provides rapid and reliable diagnosis for many musculoskeletal lesions. Due to its ease of use, absence of radiation, and cost-effectiveness, it has become a preferred modality in musculoskeletal imaging. Elastography techniques vary depending on the method of compression, tissue displacement characteristics, and image acquisition techniques. The main types used in clinical practice include strain (compression) elastography, acoustic radiation force, shear wave elastography (SWE), and transient elastography. In addition to providing morphological information, SWE allows quantitative measurement of tissue elasticity and offers valuable insights into mechanical properties related to degeneration, injury, and healing.

This technology represents an ultrasound-based counterpart of manual palpation used by clinicians for tissue characterization. SWE is one of the ultrasound elastography techniques that utilizes shear wave speed (SWS) to assess tissue stiffness. During real-time B-mode ultrasonography, localized transient displacements in the tissue are generated by short-duration acoustic push pulses, producing shear waves. The propagation speed of these waves (SWS) is then recorded.

Measurements can be expressed in meters per second (m/s) or kilopascals (kPa), depending on the system. The square root of tissue elasticity is proportional to SWS, which directly correlates with tissue stiffness. This implies that stiffer tissues allow faster propagation of shear waves. Extracellular matrix components, particularly fibrotic deposits such as collagen, are the primary determinants of tissue stiffness. Ultrasound elastography has been established as an excellent diagnostic modality for conditions such as liver fibrosis, breast cancer, and thyroid cancer. In the field of musculoskeletal medicine, numerous studies have been conducted since the early 1990s, and its clinical application has increased in recent years .

In ultrasonographic studies of lipedema, no significant differences have been observed in the dermis, whereas increased thickness and decreased echogenicity of the subcutaneous tissue have been reported . However, there are currently no studies in the literature investigating lipedema using SWE. An imaging modality that definitively supports the clinical diagnosis of lipedema has not yet been established. The diagnostic performance of existing imaging methods remains limited. Prospective studies are needed to evaluate and compare the diagnostic performance of different imaging techniques. There is also a need for imaging modalities that focus on the pathophysiology of the disease .

In this study, we aimed to compare the stiffness of lower extremity subcutaneous tissue in patients with lipedema, characterized by diffuse subcutaneous tissue expansion, with that of a healthy population using SWE. As a secondary objective, we aimed to evaluate abdominal subcutaneous tissue stiffness using SWE in patients with lipedema and to compare it with both the lower extremity measurements in lipedema patients and the abdominal subcutaneous tissue stiffness in individuals without lipedema.

Inclusion Criteria:

• Women aged ≥18 years with lipedema (stages 1-3) and healthy controls with adequate cognitive function

Exclusion Criteria:

• Age <18 years Lymphedema Edema of cardiac or nephrogenic origin Diabetes mellitus Thyroid dysfunction Oncological diseases Polyneuropathy or radiculopathy Advanced degenerative diseases affecting the extremities Use of antiepileptic or antidepressant drugs within the last 6 months Use of edema-inducing medications (e.g., corticosteroids, calcium channel blockers, gabapentin, pregabalin) Cognitive impairment preventing participation

Women aged ≥18 years with lipedema (stages 1-3) and healthy controls were included.

Women aged ≥18 years with lipedema (stages 1-3) and healthy controls were included.