 |
|
|
 |
| In the long run | |
|
--Michael
H. Brooke, M.D. |
|
|
| Although
fatty acids are not used at the beginning of exercise, they become increasingly important after 20-30 minutes of endurance exercise, and after an hour, they represent the major energy supply. Consequently defects in lipid metabolism give rise to symptoms after sustained activity. Typically, the patient with CPT II deficiency is a young adult male who experiences his first bout of weakness and myoglobinuria (dark urine) following strenuous exercise, such as mountain climbing or playing four sets of tennis. In retrospect, patients often experienced brief episodes of muscle pain as children, but these were shrugged off as growing pains or the more ordinary muscle cramps. Patients are particularly predisposed to these attacks if exercise is performed in the fasting state. This is not surprising because fasting throws the body into a dependency on fatty acids. Several patients with this illness have manifested the first symptoms during military training when they were required to undertake a forced march with a full backpack before breakfast. In disorders of lipid metabolism, attacks often occur when the patient is far away from home and must out of necessity use muscles that have already been damaged. If one is halfway up a mountain when muscle fatigue and pain occur, it is hard to stay there! Second, even when the muscle stops working, it still depends on fatty acid metabolism. Frequently, respiratory paralysis accompanies severe attacks. Patients with CPT II deficiency often notice that their stamina depends on their diet. Some will carry a candy bar to be eaten during exercise. Others know that exercise in a fasting state is far more difficult for them. Despite these limitations, most patients with CPT II deficiency are quite athletic. Usually, however, they are weight lifters or sprinters rather than marathon runners. Both activities draw on carbohydrate energy supplies and use glycolytic fibers, not the oxidative fibers. Indeed, these patients are uniformly muscular, perhaps because their favorite exercise is weight lifting. In general, laboratory studies are unrevealing of CPT II deficiency. The CK (creatine kinase) concentration may be normal unless the patient has had a recent attack of muscle damage. The muscle biopsy in CPT deficiency is normal, unless necrosis is seen associated with a recent bout of muscle damage. Biochemical analysis of the muscle biopsy reveals the deficiency of CPT, but the fact that one has to suspect the diagnosis in order to ask for the assay makes it helpful only as a confirmatory test. One useful screening test is to obtain a respiratory exchange ratio (RER). The ratio of carbon dioxide produced to oxygen consumed gives an indication of the type of fuel being used by the patient. In a normal individual at rest, the RER is approximately 0.8. This is due to the fact that fatty acids are the predominant source of fuel at rest. In CPT deficiency, the RER is seldom much below 1.0, even with the patient at complete rest. It may be worthwhile to obtain incremental bicycle ergometry results because, in addition to the RER, the VO2max and Wmax also can be determined. Both are likely to be decreased. The maximum heart rate will be normal, indicating full effort. Forearm exercise testing is not of much value in CPT II deficiency because the test stresses glycolytic pathways, and hence is normal. Patients with CPT deficiency should be cautioned to avoid any situation that provokes muscle pain and puts them at risk for myoglobinuria. |
Dr. Brooke is Director of the Muscle Disease Research Center at the University of Alberta in Edmonton. --Reprinted with permission from http://plaza.v-wave.com/mbrooke/ublish/page12.html |
|
|||
| Related
links:
Mind over Matter: The Realities of a Common Muscle Disease  CPT deficiency article by Georgirene Vladutiu, Ph.D. CPT II deficiency tutorial Interactive tutorial written by Marcel Blanchaer, M.D. Includes individual pages on muscle metabolism, the mitochondrial CPT system, fat metabolism and an extensive glossary of terms. Diagnostic Approach to Disorders of Fat Oxidation Information for clinicians by Charles Roe, M.D. Exercise Physiology Corner: Maximum Oxygen Consumption Expressing and measuring VO2max. Fat
Burning During Exercise: Can Ergogenics Change the Balance? |
|
|
|
|
|||
To read
about diagnosis experiences of CPT II deficiency patients, visit 
In spite of the fact that there is no cure for CPT II
deficiency, it is a manageable disease in most cases. It is
important that primary care physicians are informed about this
disorder and its manifestations so they can recognize the
symptoms, provide genetic testing for a diagnosis and
ameliorative treatment. Frequently patients who remain
undiagnosed wonder if their symptoms are imagined or
exaggerated because of the chronic nature of the disease. 
