Polymyositis dermatomyositis and inclusion body myositis
POLYMYOSITIS, DERMATOMYOSITIS, ANDINCLUSION BODY MYOSITIS:INTRODUCTION; The inflammatory myopathies represent the largest group of acquired and potentially treatable causes of skeletal muscle weakness. They are classified into three major groups: polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM).
POLYMYOSITIS The actual onset of PM is often not easily determined, and patients typically delay seeking medical advice for several weeks or even months. This is in contrast to DM, in which the rash facilitates early recognition. PM mimics many other myopathies and is a diagnosis of exclusion.
DERMATOMYOSITIS andINCLUSION BODY MYOSITIS DERMATOMYOSITIS DM is a distinctive entity identified by a characteristic rash accompanying, or more often preceding, muscle weakness. DM usually occurs alone but may overlap with scleroderma and mixed connective tissue disease. INCLUSION BODY MYOSITIS In patients 50 years of age, IBM is the most common of the inflammatory myopathies. It is often misdiagnosed as PM and is suspected only later when a patient with presumed PM does not respond to therapy.
ASSOCIATION WITHMALIGNANCIES The incidence of malignant conditions appears to be specifically increased only in patients with DM and not in those with PM or IBM. The most common tumors associated with DM are : ovarian cancer, breast cancer, melanoma, colon cancer, and non-Hodgkin lymphoma.
OVERLAP SYNDROMES sclerotic thickening of the dermis, contractures, esophageal hypomotility, microangiopathy, and calcium deposits
ASSOCIATION WITH VIRAL INFECTIONS Several viruses, including coxsackieviruses, influenza, paramyxoviruses, mumps, cytomegalovirus, and Epstein-Barr virus, have been indirectly associated with myositis.
Differential Diagnosis SUBACUTE OR CHRONIC PROGRESSIVE MUSCLE WEAKNESS : This may be due to denervating conditions such as the spinal muscular atrophies or amyotrophic lateral sclerosis ACUTE MUSCLE WEAKNESS : This may be caused by an acute neuropathy such as Guillain-Barr syndrome, transverse myelitis, a neurotoxin, or a neurotropic viral infection such as poliomyelitis or West Nile virus.
Treatment: Therapy of InflammatoryMyopathies1. Glucocorticoids. Oral prednisone is the initial treatment of choice;2. Other immunosuppressive drugs. Eg Azathioprine, Methotrexate3. Immunomodulation.o Calcinosis, a manifestation of DM, is difficult to treat;o IBM is generally resistant to immunosuppressive therapies. Prednisone together with azathioprine or methotrexate is often tried