Sonographic Spectrum of Rheumatoid Arthritis - An Overview

Introduction:

An autoimmune disorder is a medical condition in which the immune system attacks and kills the body's normal cells by mistake. A few common autoimmune diseases are rheumatoid arthritis, diabetes (Type 1), psoriatic arthritis, multiple sclerosis, systemic lupus erythematosus, and myasthenia gravis. Rheumatoid arthritis is a chronic inflammatory and autoimmune disorder that causes pain and swelling in the lining of the joints. It commonly affects the joints of fingers, knees, wrists, ankles, elbows, shoulders, and hips. Rheumatoid arthritis occurs at any age but is more common in middle-aged people. In addition, it is more prevalent in women than men.

What Are the Symptoms of Rheumatoid Arthritis?

The early symptoms of rheumatoid arthritis are minor joint pain, stiffness of the joints, and fatigue.

Joint Symptoms:

• Swollen joints.

• Morning stiffness.

• Joint pain is more common in the same joint on both sides.

• Joints become stiff, warm, and tender when not used for more than an hour.

Other Symptoms:

• Chest pain while breathing.

• Sjogren syndrome - An autoimmune disorder that causes dry eyes and dry mouth associated with rheumatoid arthritis.

• Burning and itching eyes, eye discharge.

• Numbness and tingling sensation in the hands and feet.

• Difficulty sleeping.

How Does Ultrasound Function?

Ultrasound is a diagnostic technique that takes images of soft tissues inside the body using sound waves. Ultrasound imaging is also called a sonogram. During the ultrasound, a manual probe called the transducer produces high-frequency sound waves that reach the organs, which rebound back and are received by the transducer. The transducer processes the reflected waves, which are then converted by the computer into images of the blood vessels. Internal structure and movements can be viewed using ultrasound. It can also show blood flowing through the blood vessels. The sound waves travel at different speeds in various tissues. It passes faster through bone tissue and slowest through the air. The speed and the amount of the sound waves reverted to the transducer determine the types of tissue.

The color and Doppler types of ultrasound play a major role in rheumatoid arthritis.

• Color Doppler- Color Doppler is a Doppler imaging in which the blood vessels appear as colored structures on the screen. This is used to determine the speed and direction of the blood flow.

• Power Doppler - This is recommended when the images are difficult to obtain with color doppler. It is used to get accurate details of the blood flow in the blood vessels inside the organs.

What Are the Uses of Ultrasonography in Rheumatoid Arthritis?

Musculoskeletal ultrasound (MSUS) is commonly used in rheumatoid arthritis. Greyscale MSUS can detect synovial proliferation, and the power Doppler can visualize neogenesis and active inflammation. The combination of power Doppler with grayscale ultrasound results in enhancement of the synovitis, which is used to visualize the bone erosions and subclinical synovitis, structural progression, and disease relapse.

Musculoskeletal ultrasound is usually performed to diagnose rheumatoid arthritis, monitor the treatment progress, and confirm the remission of the disease. Unfortunately, MSUS cannot identify the specific rheumatic disease; it can only determine the location, progress, and type of abnormalities. However, MSUS helps detect the following pathologies:

• Synovial membrane pathologies - Synovial thickening, fibrosis of the synovium, synovial sheaths or bursae, and hypervascularization.

• Exudates in synovial abnormalities.

• Tenosynovitis, swelling of the tendon, and partial or complete tendon rupture.

• Osteochondral changes - Cartilage damage, erosions, cyst, and inflammation.

• Enthesopathy is a pathology of ligament and tendon attachment.

What Are the Ultrasonographic Interpretations of Rheumatoid Arthritis?

Rheumatoid arthritis affects the synovium, subchondral bone, articular, and extra-articular adipose tissue.

Synovium:

• The synovial membrane is not visible on ultrasound in healthy individuals. Therefore, the first sign of rheumatoid arthritis is a thickening of the synovial membrane in the joint capsule at varying degrees, tendon sheath, or bursae due to hyperplasia of the inner layer of the synovial membrane, and swelling of the subintimal layer.

• Swelling of the synovial membrane appears as low echogenic, similar to the appearance of exudate on ultrasound.

• Exudate and thick inflamed (swelling) synovial membranes can be differentiated by applying pressure over the joints using a transducer. While applying the pressure, the exudate will displace, and if there is no displacement, it indicates the decompression of the joints, bursae, or sheath. It can also be differentiated with the help of power Doppler ultrasound (PDUS).

• Neoangiogenesis and synovitis are assessed by abnormal vascularization and the thickened synovium. The intensity of increased vasculature determines the severity of synovitis.

• Hyperechoic synovial membrane without vascularization indicates fibrosis resulting from radionuclide synovectomy or pharmacological treatment.

Adipose Tissue:

• In synovitis, the inflammatory cells and adipocytes release proinflammatory cytokines and growth factors that affect the synovial membrane and cartilage metabolism and result in adipose tissue swelling. Inflamed (swelling) adipose tissue appears as hyperechogenic structures.

Erosion and Subluxation:

• When the inflammatory cells infiltrate the bone marrow, they activate the osteoclast cells and damage trabeculae. This results in subchondral inflammatory cysts and erosions. When rheumatoid arthritis progresses, there is erosive destruction and the risk of subluxation and dislocation of joints.

Tendon Rupture:

• In the later stage of rheumatoid arthritis, the inflamed tendon becomes weak, resulting in a partial or complete rupture.

• Partial tendon rupture appears as an area of anechoic structures. In complete tendon rupture, the level of injury is determined by measuring the distance between the stumps and the length of the damage in tendon stumps. This is useful in reconstructive surgery.

• Dynamic ultrasound can visualize the separation of the stumps. They can also reveal abnormal tendon displacement and contracture of interphalangeal joint structures due to lack of rehabilitation. In addition, swelling of the flexor muscle-tendon sheath can result in a narrowing of the carpal tunnel called carpal tunnel syndrome.

Conclusion:

Ultrasonography is now being increasingly utilized worldwide in rheumatology. It is more sensitive in detecting synovitis in rheumatoid arthritis than clinical examination. The erosions in the early stage of rheumatoid arthritis are shown better in ultrasound than in conventional radiographs. They are also used as a follow-up investigation tool after the surgical procedure in synovitis. Musculoskeletal ultrasound can be easily performed and takes only 15 to 30 minutes to complete.