Elevated CPK and Other Diagnostic Clues to Muscle Pain
Muscle pain happens to most people. After a rigorous workout, muscles can be sore for days. That's normal muscle pain. Abnormal muscle pain is a persistent pain that does not go away with rest. The pain is deep and often unbearable. Further investigation is needed for abnormal muscle pain.
The first investigation step is laboratory tests. Pain does not accompany all muscle diseases, but an elevated creatine phosphokinase (CPK) usually does. The CPK enzyme is found in the skeletal muscles as well as the heart and brain. Non-painful causes of an elevated CPK include muscular dystrophy, dementia and motor neuron diseases. Painful conditions associated with an elevated CPK include sickle cell disease and polymyositis. Besides pain, other symptoms might provide diagnostic clues like muscle weakness which typical in polymyositis. If anemia is present, then sickle cell disease is more likely. Both polymyositis and sickle cell disease can lead to the most severe form of muscle disease called rhabdomyolysis, a wide-spread death of muscle tissue. (1)
Once a muscle disease is suspected based on an elevated CPK, what further tests can be done? In order to rule-out sickle cell disease, a hemoglobin electrophoresis test can look for hemoglobin abnormalities. That is usually only necessary for anyone born before 2006 now that all babies are tested for this painful disease. Inflammatory conditions like polymyostis will have elevated sedimentation rates (ESR), but often laboratory tests are not enough to diagnosis this disease.
After simple blood tests are done, others pieces to the diagnostic puzzle of muscle pain with high CPK are needed. The next level of diagnostic clues can be provided by electromyography and a muscle biopsy. Electromygraphy (EMG) examines the electrical active of the muscles. Abnormal activity can be due to a problem with the muscle or a problem with the nerve connected to the muscle. Taking this diagnostic investigation one step further if a muscle disease is suspected, the best diagnostic test is a muscle biopsy. Looking at the muscle under the microscope can lead to a definitive diagnosis like polymyositis. An MRI of the muscle can also be helpful especially if a specific muscle is painful and/or swollen. A condition called myonecrosis which is a rare result of sickle cell disease can be demonstrated on an MRI scan. (2)
Once enough pieces to the muscle pain puzzle are gathered, a clear diagnosis should come into focus. Some individual cases might require mores pieces than others. For example, one community member told about his diagnostic journey after an elevated CPK was discovered. Eventually, the doctor discovered that he had McArdles Disease, which means that his muscles lacked the ability to breakdown glycogen. Ultimately, please don't let anyone tell you that you have fibromyalgia with a high CPK and leave it at that answer without any further tests. If that happens, find a doctor that is willing to take a more thorough diagnostic walk with you when you have muscle pain and a high CPK.
1. Ann Indian Acad Neurol. 2009 Jan-Mar; 12(1): 45-47
2. Case Reports in Medicine, Volume 2010 (2010), Article ID 659031, 3 pages