Sarcoidosis is a rare condition, characterized by clumps of inflammatory immune cells, called granulomas, that form in various organs and tissues. Their accumulation affects the organ’s ability to work as needed, and causes inflammation. If untreated, permanent organ damage can result.
Multiple types of sarcoidosis are known, based on where the granulomas form and the organs and tissues affected, and a sarcoidosis patient can have more than one type.
Musculoskeletal sarcoidosis refers to disease impacts and risks damage to the bones, muscles, or joints.
What is musculoskeletal sarcoidosis?
Musculoskeletal sarcoidosis is associated with granulomas building up in one or more parts of the musculoskeletal system; it can affect the joints, muscles, or bones.
Joint involvement is one of the most common features of musculoskeletal sarcoidosis, with around 10 to 35 percent of these patients showing arthritis-like symptoms. This can be caused by joint inflammation, restricting a patient’s range of movement and causing pain.
The majority of cases are associated with acute polyarthritis, where symptoms are generally mild, start suddenly, and can resolve without treatment. The ankles are the most commonly affected joint, followed by the other joints of the lower limbs. Löfgren’s syndrome is a mild type of acute arthritis seen in sarcoidosis, associated with swelling of the joints and painful bumps on the shins, called erythema nodosum.
Chronic arthritis is rare in sarcoidosis, affecting less than 1 percent of patients. However, it tends to be more severe and usually requires treatment to prevent permanent damage to the joints. Chronic arthritis in sarcoidosis patients typically affects the ankles, feet, knees, wrists, or hands.
Bone involvement, or osseous sarcoidosis, is rare and often without symptoms. Inflammation in the bones can result in some patients developing dactylitis, inflammation of the digits, in the small bones of the fingers and feet, often accompanied by lupus pernio. Dactylitis can result in the bones having a “lacy” pattern under X-ray.
Sarcoidosis may also affect bone density, lead to an increased risk of fractures should bones weaken. Loss of bone density can also be a side effect of the corticosteroid therapy often used to treat sarcoidosis.
Granulomas may be present in the muscle of around 50-80 percent of sarcoidosis patients. But troublesome symptoms are rare, affecting about 1 percent of these patients. In these cases, granulomas can build to form a painful tumor-like lump that can compress and damage surrounding muscle tissue.
Symptoms of musculoskeletal sarcoidosis
Although musculoskeletal sarcoidosis is often asymptomatic, patients may experience such symptoms as:
- joint pain
- rigid or stiff joints
- erythema nodosum
- muscle weakness (myopathy)
- muscle pain
Diagnosis of musculoskeletal sarcoidosis
There is no single test to diagnose musculoskeletal sarcoidosis. If a patient is known to have sarcoidosis and is having common symptoms of musculoskeletal sarcoidosis, reports and observations support a diagnosis.
As musculoskeletal sarcoidosis is asymptomatic in many cases, a patient may not be diagnosed until a different sarcoidosis manifestation is identified or a test for an unrelated condition detects it.
Commonly, a musculoskeletal sarcoidosis diagnosis will involve one or more imaging tests. These allow the affected area to be visualized and can be used to detect joint inflammation or to confirm the presence of nodules in the muscles. Imaging techniques used include magnetic resonance imaging (MRI), computed tomography (CT) scans, X-rays, ultrasound, or positron emission tomography (PET).
A small tissue sample, or biopsy, may also be taken from an affected muscle or swollen joints to be examined for abnormalities commonly seen in sarcoidosis.
Electromyography (EMG), where a small electrical pulse is delivered to an affected muscle, may also be used to confirm muscle abnormalities or weakness.
Blood tests may be taken as patients can have elevated levels of certain enzymes, such as angiotensin-converting enzyme (ACE), creatine kinase, or aldolase. Blood tests are not able to reach a definitive diagnosis however, as many patients will have these enzymes at normal blood levels.
Treatment of musculoskeletal sarcoidosis
For severe or chronic joint involvement, or where NSAID or corticosteroid therapy is not possible or not recommended, the patient may be prescribed treatments that suppress the immune system. These include methotrexate, Imuran (azathioprine), or tumor necrosis factor alpha inhibitors (anti-TNFalpha).
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