Dermatomyositis (DM) is an inflammatory musculoskeletal condition with a constellation of clinical findings, including weakness of the proximal skeletal muscles, skin rash, and elevated muscle enzymes.
DM is challenging to diagnose and is usually done using laboratory studies (eg aldolase and creatinine kinase) and histopathology from a muscle and/or skin biopsy.
Once a patient is diagnosed with DM, he or she can be treated with a multitude of medications including steroids, methotrexate, azathioprine, and intravenous immune globulin (IVIG).1
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In addition to frequent monitoring of labs and the patient’s improvement during physical exam, patients with DM must be monitored closely for potential malignancies, as there is an increased risk of cancer, particularly within the first 5 years after symptom onset. The most common cancers seen in patients with DM include breast, colon, lung, ovarian, melanoma, non-Hodgkin lymphoma (NHL), nasopharyngeal, and stomach.2-4
The overall cancer rate in patients with DM varies between 9% and 32%.
The highest risk of developing cancer in patients with DM is within the first year of onset of myositis. Older patients, those with more severe findings on skin/muscle biopsy (cutaneous necrosis, capillary damage, and cutaneous leukocytoclastic vasculitis), prior history of cancer, and treatment resistance are at high risker of developing cancer within the DM population.
Patients should be up to date with all age and gender-appropriate screenings, such as mammography, pelvic exam, Pap test, and colonoscopy. If the patient has not had recent blood work, he or she should have basic labs drawn, including comprehensive metabolic panel and complete blood count.
It is important to review a patient’s recent DM-specific labs, as particular antibodies can provide insight into cancer risk. The cancer-associated myositis (CAM) antibody is linked with increased cancer risk, though patients positive for additional antibodies actually have a lower risk of developing malignancy (anti-SRP, anti-synthetase, anti-Mi-2, anti-RNP, anti-Ku, and anti-PM-Scl).
Depending on age and smoking history, screening for lung cancer should also be considered. It is not recommended, however, to send extensive tumor markers such as CEA, CA 19-9, CA 125, and CA 15.3, unless clinically warranted.
Women at risk for ovarian cancer should undergo a transvaginal ultrasound.
Patients may also need contrast-enhanced cross sectional imaging such as computed tomography (CT) of chest, abdomen, and/or pelvis. If the patient initially responds well to treatment and subsequently becomes refractory, the potential for newly undiagnosed malignancy should be considered.
The exact pathophysiology explaining the connection between DM and cancer is not entirely known, though it may have to do with the pro-inflammatory state associated with the overriding autoimmune reaction to skeletal muscle tissue.
Treating physicians should watch for any suspicious signs of cancer after DM is diagnosed.
References
- Dalakas MC. Inflammatory Muscle Diseases. N Engl J Med. 2015;372(18):1734-47. doi: 10.1056/NEJMra1402225
- Hill CL, Zhang Y, Sigurgeirsson B, et al. Frequency of specific cancer types in dermatomyositis and polymyositis: a population based study. Lancet. 2001;357:96-100.
- Chen YJ, Wu CY, Huang YL, Wang CB, Shen JL, Chang YT. Cancer risks of dermatomyositis and polymyositis: a nationwide cohort study in Taiwan. Arthritis Res Ther. 2010;12(2):R70. doi: 10.1186/ar2987
- Levine SM. Cancer and myositis: new insights into an old association. Curr Opin Rheumatol. 2006;18(6):620-4.
