Autoimmune diseases often express similar symptoms in different conditions. This is one of the reasons it is so difficult to diagnose these diseases. Dermatomyositis and lupus, for example, both have a characteristic rash over the bridge of the nose. Patients with antisynthetase syndrome experience the same Raynaud’s phenomenon as those with scleroderma.

Sometimes, however, patients can experience the whole range of clinical symptoms and laboratory findings of two well-defined autoimmune diseases at the same time—even those that are not part of one or the other disease. When this happens, they are said to have overlap syndrome. Myositis overlap syndromes tend to appear more in patients with dermatomyositis, polymyositis, and necrotizing myopathy.

Common conditions that tend to occur together with myositis include the following:

Systemic sclerosis (scleroderma) is the most common overlapping disease with myositis. It is a progressive disease of skin and connective tissue (cartilage, bone, fat, and the tissues that support the nerves and blood vessels). It is caused by the accumulation of collagen (a structural protein) in the inner walls of the small arteries that causes skin and the tissues of internal organs to become sclerotic (thickened, hardened).

Rheumatoid arthritis (RA) is a systemic autoimmune disease that causes inflammation and deformity in many joints throughout the body. It can also involve other organs, especially in patients who are not treated.

Systemic lupus erythematosus (SLE or lupus) is a chronic autoimmune disease that damages tissue in many parts of the body, including skin, joints, lungs, and kidneys. Some of the symptoms of lupus include hair loss, mouth ulcers, swollen lymph nodes, fatigue, and a characteristic red rash that spreads over the cheeks and nose.

Sjögren’s syndrome is an immune-mediated destruction of the endocrine glands, most prominently the tear and salivary glands, causing dry eyes and dry mouth. Other glands and organs can also be affected.

Other conditions similar to overlap syndrome

Mixed connective tissue disease (MCTD) is a syndrome that involves a variety of manifestations of several different autoimmune diseases without definitive diagnostic features of any one disease.

Undifferentiated connective tissue disease (UCTD) is a syndrome that presents with several symptoms of various autoimmune diseases, but not enough features to define it as a single disease or to define it as MCTD. Sometimes patients will eventually be diagnosed with one disease; other times their disease remains undifferentiated.

Autoantibodies and overlap syndrome

Autoantibodies can be very important in diagnosing these autoimmune diseases. Some antibodies are associated with specific overlapping diagnoses, including:

Mixed connective tissue disease –  anti-RNP

Polymyositis/scleroderma overlap –  anti-PM/SSc

Polymyositis/scleroderma overlap – anti-Ku

Myositis/lupus overlap – anti-DsDNA and anti-Sm

Myositis/Sjögren’s – anti-SSA

Antisynthetase syndrome – anti-Jo-1

Treatment of overlapping diseases involves immunosuppression, but the choice of medications is guided by the clinical features in a particular patient and tailored to the most severe or major disease manifestations. Medications that may be effective for various features of overlapping diseases include:

Corticosteroids for inflammatory conditions, especially myositis

Imuran and methotrexate for muscle disease

Methotrexate and anti-TNF inhibitors for arthritis

CellCept for skin

CellCept or tacrolimus for lungs

Additional information about overlapping autoimmune diseases can be found in the Myositis Library section of this website.

When you have more than one disease – A presentation by Dr. Rohit Aggarwal at the TMA Annual Patient Conference