Case 2
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.
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.
The Tips
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.
Case 3
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.
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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
