A 38-year-old man had seen a skin rash on his hand, along with arthralgia, in August of 2004. By November, he’d developed a cough and breathlessness. Those symptoms had worsened within a few months, and he’d developed mild muscle weakness, too.
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Tests found his CK levels were normal. He was also found to have interstitial lung disease (ILD), which was rapidly progressing, and the man was positive for SSA/anti-Ro antibodies.
He was found to be major histocompatibility complex (MHC) class I positive on muscle fibers in the muscle biopsy investigated by immunohistochemistry, as well as positive for anti-MDA5, an antibody recently found to be associated with dermatomyositis, which was determined to be the patient’s diagnosis.
Dr. Lundberg said that a normal CK and normal histopathology do not exclude dermatomyositis, and that an MRI and testing for myositis-specific antibodies can be helpful.
More specifically, this patient could be classified as having clinically amyopathic dermatomyositis, with a skin rash typical of dermatomyositis, but combined with rapidly progressing ILD and the presence of anti-MDA5 antibodies.
She also said a link between ILD and myositis has been increasingly recognized, with ILD in 60% to 70% of dermatomyositis and polymyositis cases—and, in fact, it might be the first clinical symptom of myositis. Anti-MDA5 antibodies may be associated with a rapidly progressive ILD.
Another similar subgroup is antisynthetase syndrome, characterized by ILD, myositis, arthritis, fever, Raynaud’s disease, and an association with the HLA-DRB1 allele. It can be found in dermatomyositis and polymyositis. Eight antibodies are linked with this subgroups—the most common is anti-Jo-1.
At about age 44, a man was diagnosed with polymyositis. He had developed atrial fibrillation from the time he was 35; by 44, he had arm and leg weakness, along with myalgia. A muscle biopsy had found degenerating and regenerating fibers but no inflammatory cell infiltrates, and he was MHC class I positive in his muscle fibers.
He was treated, but at age 57, he still had profound muscle weakness, and had developed swallowing problems and atrophy of the hamstrings, but a muscle biopsy from the quadriceps is normal.
The man was then found to be antinuclear antibody negative but anti–signal recognition particle positive and was diagnosed with immune-mediated necrotizing myopathy, a disorder characterized by cardiac involvement and treatment-resistant myositis.
Dr. Lundberg said it’s important to be aware of cancer-associated myositis. No particular kind of cancer is overrepresented, and there are no specific clinical features to look for. But, she said that if a dermatomyositis is treatment resistant, an underlying malignancy should be considered. There is an association with the anti–TIF1 gamma antibody, which is not yet commercially available.1