If it affects the blood vessels in the stomach or intestines, which is more common in juvenile DM, the people might vomit blood, have black tarry bowel movements, or may develop a hole somewhere in their GI tract.There are further complications possible with Dermatomyositis. These complications include difficulty swallowing due to the muscles in the esophagus being affected which can result in malnutrition and can cause the breathing of food or liquids, into the lungs. Examples of dermatomyositis

Causes
The cause is unknown, but it may result from an initial viral infection or cancer, either of which could raise an autoimmune response.Between 7 and 30% of dermatomyositis cases arise from cancer, probably as an autoimmune response. The most commonly associated cancers are ovarian cancer, breast cancer, and lung cancer. Between 18 and 25 per cent of people with amyopathic DM also have cancer. Malignancy in association with dermatomyositis is more prevalent after age 60. Some cases are inherited, and HLA subtypes HLA-DR3, HLA-DR52, and HLA-DR6 seem to create a disposition to autoimmune dermatomyositis.
Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may include weight loss, fever, lung inflammation, or light sensitivity. Complications may include calcium deposits in muscles or skin.The cause is unknown. Theories include that it is an autoimmune disease or a result of a viral infection. Dermatomyositis may develop as a paraneoplastic syndrome associated with several forms of malignancy. It is a type of inflammatory myopathy. Diagnosis is typically based on some combination of symptoms, blood tests, electromyography, and muscle biopsies.While no cure for the condition is known, treatments generally improve symptoms. Treatments may include medication, physical therapy, exercise, heat therapy, orthotics and assistive devices, and rest. Medications in the corticosteroids family are typically used with other agents such as methotrexate or azathioprine recommended if steroids are not working well. Intravenous immunoglobulin may also improve outcomes. Most people improve with treatment and in some, the condition resolves completely.About one per 100,000 people per year are newly affected. The condition usually occurs in those in their 40s and 50s with women being affected more often than men. People of any age, however, may be affected. The condition was first described in the 1800s. Signs and symptoms
The main symptoms include several kinds of skin rash along with muscle weakness in both upper arms or thighs.