Muscular Arthritis Is Rare, but There Are Symptoms Everyone Should Know

You know how tuna is sometimes called "chicken of the sea?" They're different foods, of course, but the comparison helps make the unfamiliar seem a little more ordinary. Well, the same logic applies to the term muscular arthritis.

Just like chickens don't come from the sea, arthritis doesn't occur in your muscles. The word literally means joint (arth) inflammation (itis). But muscular arthritis is a term some people use for a chronic autoimmune condition more formally known as myositis, which is marked by muscular (myo) inflammation, says Timothy Gibson, MD, orthopedic surgeon and medical director of the MemorialCare Joint Replacement Center at Orange Coast Medical Center in Fountain Valley, California.

Read on to learn more about the condition, what causes it and what treatment options are available.

Technically speaking, myositis occurs anytime a muscle is inflamed, like when you injure it with overuse, according to The Myositis Association. But most of the time, experts use the term to refer to a condition in which the muscles are attacked by the immune system, explains Paul Twydell, DO, a board-certified neurologist in Michigan.

Myositis typically leads to muscle pain — also known as myalgia — and weakness, Dr. Twydell tells LIVESTRONG.com. The symptoms usually occur in the shoulders and hips, but any muscle group may be affected. Myositis can affect both adults and children.

Myositis can be broken down into three specific types:

1. Sporadic Inclusion Body Myositis: This is the most common type of myositis, characterized by progressive muscular weakness, and it's most often seen in people over the age of 50. "It progresses slowly and sometimes is present for many years before it is diagnosed," Dr. Gibson says. Early symptoms include trouble standing from a chair, difficulty climbing stairs and a weak grip.

2. Dermatomyositis: This type occurs in people of all ages but is more common in young women. It involves inflammation of the muscles, but individuals who have it will also develop a rash that appears on the eyelids, cheeks, nose, back, upper chest, elbows, knees and knuckles, Dr. Gibson says.

3. Polymyositis. Again more common in women, this type typically occurs in people over age 20. Symptoms include muscle weakness starting on the trunk — including the neck, shoulders and hips — that can worsen over time and affect the muscles of the entire body.

There are two additional types of myositis that are more rare: necrotizing myopathy, in which muscle cells die off, causing weakness and fatigue, and juvenile myositis, which affects children under the age of 18 and is characterized by muscle weakness and a red, patchy skin rash.

All types of myositis are considered to be inflammatory myopathies, which are very rare, affecting just 50,000 to 75,000 people in the U.S., according to The Myositis Association.

"This is a one in a million condition," Victoria Seligman, MD, MPH, a rheumatologist at UCHealth Rheumatology Clinic – Cherry Creek in Denver, Colorado, tells LIVESTRONG.com.

The primary symptoms of myositis are:

• Muscle weakness
• Swelling
• Muscle pain (some cases)
• Rash over the face, chest, back and/or joints, such as the bony parts of the hand (some types)

According to The Myositis Association, symptoms usually come on quite gradually and those with the condition might first notice smaller signs, such as:

• Having trouble climbing stairs
• Difficulty holding onto a cup while drinking
• Trouble swallowing
• Difficulty walking
• Premature muscle fatigue
• Problems with muscle relaxation
• Generalized fatigue

There are often other complications that coincide with myositis, such as infection, cancer or other autoimmune disorders like lupus.

Because of this, along with the fact that it's a rare condition and has broad symptoms, myositis can be difficult to diagnose.

"Myositis is an uncommon but sometimes disabling condition," Dr. Gibson says. "If you have unexplained muscle pain and weakness, including new-onset trouble standing from a chair, you may have myositis."

The vast majority of myositis cases are autoimmune conditions, meaning the body forms antibodies against the muscle tissue, Dr. Twydell says. Exactly why that happens is still unclear.

Less commonly, myositis can also be caused by an underlying condition such as cancer, rheumatological diseases or certain medications, like cholesterol medications.

Because myositis is an autoimmune disorder, it's treated with medications that will suppress or "quiet" the immune system.

Typically, these involve steroids like prednisone, immune-suppressing drugs like mycophenolate, azathioprine or methotrexate, or immune-modulating drugs such as intravenous immunoglobulin (IVIg) or rituximab. Dr. Twydell notes that there are several new medications being studied as well.

Outside of medications, things like physical therapy and massage can help manage symptoms once the inflammation is under control. Avoiding triggers that may worsen symptoms and maintaining a healthy lifestyle in general can help as well, notes Dr. Seligman.

For example, Dr. Twydell says that following an anti-inflammatory diet may play a role in reducing some of the disease burden. And regular physical exercise is recommended as part of a myositis treatment plan, according to Dr. Gibson.

"The goal is to reduce inflammation, reduce fatigue, increase stamina and build muscle," he explains. "Dietary goals include consumption of foods that minimize inflammation, including avoidance of simple sugars."

Because myositis can be a difficult condition to diagnose, Dr. Twydell urges anyone who experiences symptoms of muscle weakness to visit their doctor for further evaluation, and don't be afraid to seek a second opinion. A doctor may order blood tests, perform an electrical test on the muscles (EMG) or take a muscle biopsy to confirm the diagnosis.

"Once the diagnosis is made, patients will typically get relief from one of the above treatments fairly rapidly," Dr. Twydell says.

However, because of the complexities of the conditions, it is best managed by an expert in muscle diseases like a neurologist or rheumatologist.

"If there are any suspicions, get a rheumatologist involved very early," Dr. Seligman says, adding that rheumatology partners with many other specialties to help manage the condition. "Myositis is a disease that requires a team."