Muscle Weakness Abnormal Gait or Difficulty Walking Elevated Creatine Kinase Respiratory Insufficiency Difficulty Swallowing Exercise Intolerance
2.7 to 70 per 100,000
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Pompe disease
2.5 per 100,000
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  • Polymyositis is a disease of the muscles characterized by chronic muscle inflammation (an inflammatory myopathy) that causes weakness in the upper arms and upper legs
  • Some signs and symptoms of polymyositis may overlap with those of Pompe disease

Signs and Symptoms

  • Like Pompe disease, patients with polymyositis generally experience weakness in the proximal muscles, which are the muscles of the upper arms, shoulder, upper legs, and hip
  • The symptoms may worsen over time, and muscles farther away from the abdomen, including those in the lower arms and legs, hands, and feet, may become affected
    • Symptoms of muscle weakness can include difficulty standing from a seated position, climbing stairs, lifting objects, or raising the arms above the head
  • Patients with polymyositis may also experience arthritis, shortness of breath, difficulty swallowing or speaking, mild joint or muscle tenderness, and heart rhythm irregularities


  • Unlike Pome disease, it is not known if polymyositis is caused by alterations in any specific gene
  • Some of the tests used to diagnose Pompe disease can also be used in the diagnosis of polymyositis, including electromyography (used for studying the electrical activity of the muscles) and laboratory testing (e.g., creatine kinase)
  • Polymyositis differs from Pompe disease because it can also be diagnosed by the detection of autoantibodies specific to an associated autoimmune response

The information presented is intended as a brief overview. It is not an exhaustive summary of polymyositis. For more information on polymyositis, visit:https://rarediseases.info.nih.gov/diseases/7425/polymyositis

For more information on the diagnosis of Pompe disease, visit Diagnostic Journey: Infantile-Onset Pompe Disease and Diagnostic Journey: Late-Onset Pompe Disease