Sarcoid Arthropathy- Causes, Types, Symptoms, Diagnosis, and Treatment

Introduction:

The functioning of the human body is quite complex to understand. It is a known fact that the body has defensive mechanisms to fight against foreign invaders. Contrary to this, the human body can actually attack its own cells. This happens when the body can not differentiate between foreign cells and native cells. The diseases that manifest due to the immune system attacking healthy cells in the body are known as autoimmune diseases. One such disease called sarcoidosis develops due to abnormal deposition of the inflammatory cells in the form of lumps. These lumps, known as granulomas, begin to affect multiple organs. Sarcoid arthropathy is a type of arthritis (inflammation of joints) that occurs as a manifestation of sarcoidosis.

What Is Sarcoid Arthropathy?

Patients diagnosed with sarcoidosis can display symptoms of arthropathy (joint disease). Although sarcoidosis is a multisystem disease, its association with joint inflammation has been significant. Generally, inflammatory arthritis causes extreme pain in the joints due to inflammation. The culprit behind these inflammatory changes in sarcoid arthropathy is sarcoidosis. A decent proportion of the patients with sarcoidosis show joint involvement in the form of arthritis and arthropathies. The terms sarcoid arthritis and sarcoid arthropathy are used interchangeably.

How Does Sarcoid Arthropathy Occur?

The etiology behind this condition has still been a mystery. Although sarcoid arthropathy is postulated as a manifestation of an autoimmune disease (sarcoidosis in this case), the reason is not fully understood yet. Some pieces of evidence lean towards environmental, infectious, and genetic factors. The autoimmune response could be triggered due to these factors mentioned above. As of now, researchers have established strong links between HLA (human leukocyte antigen) and the proteins that help in immune system regulation.

Is Sarcoid Arthropathy a Common Condition?

Approximately 15 % to 25 % of people with sarcoidosis experience sarcoid arthropathy during the initial stages of the disease. Most often, lungs, skin, and eyes are involved. However, the musculoskeletal symptoms may not be distinct. Symptoms are nonspecific and may be superimposed with symptoms of other autoimmune conditions like rheumatoid arthritis. In a proportion of patients (around 38 %), arthritis may manifest during the subsequent follow-ups. Women are more affected than men. This disease peaks between the age of 20 to 40 years.

What Are the Types of Sarcoid Arthropathy?

Clinically, two subtypes of sarcoid arthritis or sarcoid arthropathy exist, acute and chronic forms. The acute form of joint involvement is more common than the chronic form.

A. Acute Sarcoid Arthritis:

More than 70 to 80 % of patients develop symptoms of acute sarcoid arthritis. The acute form may be present during the initial diagnosis or during later stages. The striking feature is the involvement of ankles (in 90 % of patients). Other larger joints of extremities like knee and wrist joints may be involved. The symptoms of acute sarcoid arthropathy may be migratory (pain moves from one joint to another). The pain may also be intermittent or continuous. A clinical presentation of systemic sarcoidosis called Lofgren's syndrome involves a triad of arthritis of large joints, particularly ankles, bilateral hilar lymphadenopathy (enlargement of lymph nodes located in the lungs), and erythema nodosum (inflammation of the fatty layer of skin). Clinicians diagnose acute sarcoid arthropathy based on these four characteristic features:

1. Erythema nodosum.

2. The duration of symptoms is less than two months.

3. Age less than 40 years.

4. Involvement of both the ankles.

B. Chronic Sarcoid Arthritis:

A minor cohort of patients experience chronic sarcoid arthritis. In chronic sarcoid arthropathy, medium to large-sized joints are involved, in contrast to acute sarcoid arthropathy, which usually involves large joints. The frequently affected sites include metacarpophalangeal (joints connecting hand, wrist, and fingers), interphalangeal (joints between the fingers), hands and wrist, and rarely temporomandibular joints.

The following four clinical subtypes of chronic sarcoid arthropathy have been identified.

• Jaccoud’s Type Deformity (Non-erosive Joint Deformity) - Deformation of the joints due to inflammation.
• Joint Swelling - Usually seen adjacent to a sarcoid bone lesion.
• Dactylitis - Sausage-like swelling of one or more digits due to severe inflammation.
• Gouty Arthritis (Acute and Chronic) - Joint inflammation due to deposition of uric acid crystals in the joints.

What Are the Symptoms of Sarcoid Arthropathy?

A. Joint Pain - Joint pain is the most common presenting complaint. It may involve multiple joints due to inflammation and joint damage.

B. Joint Stiffness - Joints may feel stiff, causing immobility and tightening of muscles around the joint.

C. Joint Swelling - Due to the inflammatory fluid build-up, joints get swollen, which may lead to permanent damage.

D. Redness Around the Joints - Joints may appear red due to inflammation which causes dilation of the blood vessels.

E. Deformity of the Joints - Mostly occurs in the smaller joints of the hand's wrist due to weakened ligaments.

How Is Sarcoid Arthropathy Diagnosed?

The diagnosis of sarcoid arthropathy is established after taking a thorough history of symptoms, clinical findings, and lab findings.

1. Conventional Radiographs - Plain radiographs of the joints reveal soft tissue swelling and osteoporosis (brittle and weak bones), and joint space narrowing.

2. Ultrasonography - Shows joint effusion (extra fluid around the joints), synovial thickening (tissues lining the joints), and hypervascularity (increased blood supply).

3. MRI (Magnetic Resonance Imaging) - It is a more useful diagnostic tool that displays inflammation of the synovial membrane.

4. Biopsy - Soft tissue biopsy is needed to confirm the diagnosis.

What Is the Treatment for Sarcoid Arthropathy?

In general, there is no approved treatment for sarcoidosis-induced arthropathy. The treatment is symptomatic and involves multiple groups of drugs. However, it is essential to note that symptoms of arthropathy are self-limiting, and it disappears gradually. Assessment of the response to medication should be periodically monitored. The symptoms can be managed during occasional flare-ups by using the following medications.

1. NSAIDs (Non-steroidal Anti-inflammatory Drugs) - These are the first line of drugs used to reduce pain and inflammation of the joints. They do not treat the underlying condition but rather help reduce the severity of symptoms. Some commonly used NSAIDs are Aspirin, Ibuprofen, Celecoxib, Indomethacin, etc.

2. Steroids - Low doses of steroid preparations are given systemically or orally. Steroids help by reducing inflammation and also by suppressing the hyperactive immune system. The most commonly used steroids are Prednisone, Hydrocortisone, Dexamethasone, etc.

3. Antimetabolites - Antimetabolites are drugs that interfere with metabolic activities. Methotrexate is one such drug used if the patients are not responding to steroids. It has been proven effective and reduces the severity of the disease significantly.

Conclusion:

Sarcoid arthropathy is a rare manifestation of systemic sarcoidosis. The reason for this occurrence is thought to be autoimmune in origin. Two patterns of the disease are observed in acute and chronic forms. Both show joint inflammation symptoms like pain (especially in the ankles), swelling, redness, etc. The diagnosis is made after a thorough clinical and radiographic examination. Treatment usually involves symptomatic management with NSAIDs and steroids. In more severe cases, Methotrexate is the drug of choice. Sarcoidosis is a complex multisystem disease that requires a multidisciplinary approach. More research and studies would help in understanding and management of this condition.