Often patients with metabolic defects are misdiagnosed due to misinterpretation of laboratory data or symptoms with abnormalities attributed to psychological factors, to non-neuromuscular diseases, or to an inflammatory myopathy. The most common error is to consider the patient's symptoms of exercise intolerance to derive from poor motivation.

The first element in the diagnosis of metabolic myopathies is recognition of a compatible history. If the history reveals a typical pattern, appropriate diagnostic testing can be performed as a means of determining if in fact the patient has a metabolic myopathy and where and to what extent the breakdown occurs.

The following are brief descriptions of the testing performed by the Neuromuscular Center. Since each patient and their history are evaluated individually, determination of the test(s) to be performed is based on the patient's symptoms and suspected diagnosis.  The Physician will first explain the testing, and the patient signs a disclosure form confirming that the patient understands the procedures.

VENOUS CATHETER PLACEMENT
The tests require that blood samples be taken. Therefore, a thin plastic tube called a venous catheter will be inserted into a vein prior to testing to avoid repeated punctures.

ISCHEMIC FOREARM EXERCISE TEST
A blood pressure cuff is inflated on your arm prior to exercise which will cause temporary ischemia by inhibiting the flow of blood to the working forearm muscle. You will be asked to squeeze and release a handgrip device on and off for approximately one minute and blood samples are drawn to measure the accumulation of metabolites released by the muscle into the blood stream following this anaerobic exercise. Additional data is gathered that will be analyzed by the exercise physiologist and your doctor.

CYCLE EXERCISE TEST
This is a symptom limited maximal exercise test using a stationary bicycle. You will exercise at several workloads on a bicycle ergometer so we can measure the effects of exercise stress on your body. Data will be collected first while you rest in a chair. Subsequently, you will ride the cycle for approximately 20 minutes. Your blood pressure and heart will be monitored with a 12-lead electrocardiogram before, during, and after exercise. Your blood will be drawn approximately six times from the venous catheter in your arm. During different intervals of the test, you will be asked to place a snorkel-type mouthpiece in your mouth, and we will collect expired air so we can measure the quantity of oxygen your body is using. Then, you will breath a small concentration of harmless gases (oxygen, helium, acetylene) for approximately 15 seconds so we can measure cardiac output. Exercise will be stopped immediately if there are any signs of over strain.

NEEDLE MUSCLE BIOPSY
A needle biopsy is the removal of a small piece of muscle (less than the size of a pea) from your thigh for biochemical analysis.

SKIN BIOPSY
A skin biopsy is removal of a small piece of skin tissue by surgery. The tissue is then examined in the laboratory. Patients suspected of having an enzyme deficiency can be diagnosed by having cultured fibroblasts grown from a skin biopsy.

MAGNETIC RESONANCE SPECTROSCOPY
Knee extension exercise will be performed in an MRI magnet to assess muscular energy metabolism by using magnetic fields to detect phosphorus compounds in muscle.

NEAR INFRARED SPECTROSCOPY
A handgrip device will be squeezed at various intensities while a light is directed onto your arm. This procedure permits estimation of relative levels of oxygenated and deoxygenated hemoglobin and myoglobin under the beam of light.