Polymyositis

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Polymyositis
Classification & external resources

DiseasesDB	10343
MedlinePlus	000428
eMedicine	med/3441  emerg/474

Polymyositis is a type of inflammatory myopathy, related to dermatomyositis and inclusion body myositis. Polymyositis means 'many muscle inflammation'.

Polymyositis tends to become evident in adulthood, presenting with bilateral proximal muscle weakness, often noted in the upper legs due to early fatigue while walking. Sometimes the weakness presents itself by the person being unable to rise from a seated position without help, or inability to raise their arms above their head. The weakness is generally progressive, accompanied by lymphocytic inflammation (mainly cytotoxic T8 lymphocytes). The cause is unknown, but seems to be related to autoimmune factors, genetics, and perhaps viruses. In rare cases, the cause is known to be infectious, associated with the pathogens that cause Lyme disease, toxoplasmosis, and others.

Polymyositis, like dermatomyositis, strikes females with greater frequency than males. The skin involvement of dermatomyositis is absent in polymyositis.

Diagnosis is fourfold, including elevation of creatine kinase, signs and symptoms, electromyograph (EMG) alteration, and a positive muscle biopsy. Treatment generally involves glucocorticoids, especially prednisone. At present, a number of studies are underway to determine whether patients diagnosed with polymyositis will benefit from newer drugs inhibiting the biologic effects of TNF alpha, such as Infliximab ("Remicade").

Sporadic inclusion body myositis (sIBM): IBM is often confused with (misdiagnosed as) polymyositis and polymyositis that does not respond to treatment is likely IBM. sIBM comes on over months to years, polymyositis comes on over weeks to months. It appears that sIBM and polymyositis share some common features, especially the initial sequence of immune system activation, however, polmyositis does not display the subsequent muscle degeneration and protein abnormalities as seen in IBM. As well, polymyositis tends to respond well to treatments, IBM does not. IBM and polymyositis apparently involve different disease mechanisms than are seen in dermatomyositis.

v • d • e Muscular Dystrophy
The Nine Primary Muscular Dystrophies
Becker's • Congenital • Duchene • Distal • Emery-Dreifuss • Facioscapulohumeral • Limb-girdle muscular dystrophy • Myotonic • Oculopharyngeal
Other diseases generally classified as Muscular Dystrophy
Spinal Muscular Atrophies	Amyotrophic lateral sclerosis • Infantile Spinal Muscular Atrophy • Intermediate Spinal Muscular Atrophy • Juvenile Spinal Muscular Atrophy • Adult Spinal Muscular Atrophy
Inflammatory Myopathies	Dermatomyositis • Polymyositis
Diseases of Peripheral Nerve	Charcot-Marie-Tooth disease • DeJerine-Sottas Disease • Friedreich's Ataxia
Diseases of the Neuromuscular Junction	Myasthenia gravis • Lambert-Eaton myasthenic syndrome
Metabolic Diseases of the Muscle	Acid Maltase Deficiency • Carnitine Deficiency • Carnitine Palmityl Transferase Deficiency • Debrancher Enzyme Deficiency • Lactate Dehydrogenase Deficiency • Mitochondrial Myopathy • Myoadenylate Deaminase Deficiency • Phosphorylase Deficiency • Phosphofructokinase Deficiency • Phosphoglycerate Kinase Deficiency
Less Common Myopathies	Central Core Disease • Hyperthyroid Myopathy • Myotonia Congenita • Myotubular Myopathy • Nemaline myopathy • Paramyotonia Congenita • Periodic paralysis
Organizations and National events
Muscular Dystrophy Association • Jerry Lewis MDA Telethon • National Institute of Neurological Disorders and Stroke • National Institute of Arthritis and Musculoskeletal and Skin Diseases