10 year-old for muscle biopsy...

I have a 10 year-old son who will undergo a muscle biopsy in 3 days.   Four years ago he began complaining of leg/thigh pain with exertion.  When he began crying with the pain, I took him to the doctor who said it was 'growing pains'.  Since that time, he has been involved in baseball.  Although he is a good hitter, he could very rarely make it to 3rd base. By the time he got past second base, his head was tilted back, arms hanging down to his sides, and dragging his feet.  He was in excruciating pain and crying.  Doctor still said growing pains. Now he is in basketball where the symptoms/pain are more apparent. He could not keep up with the others.  He could not do 5 laps, but only 3 laps, then he was on the floor crying holding his legs.  After short rest, he could go again but the pain returned with the same amount or less exertion.  Multiple x-rays were normal.  Then we did blood work which showed an elevated CPK. He was sent to a specialist who did more bloodwork (3 tests in 2 weeks all results were within 2700~3200 range)  The specialist immediately arranged for my son to have a muscle biopsy.  I am wondering what kinds of questions I should ask regarding the biopsy.  I am wondering what the muscle biopsy can tell us.  What types of muscular diseases could my son have or could there be some other reason for his CPK to be elevated.  Can genetic testing be done through the biopsy?  From my own research, it sounds most like phosphorylase deficiency (McArdle's disease) with which certain anesthesia can be fatal.  I am scared about the anesthesia part...should I be?

[CCF-Neuro-M.D.-CS]

I cannot make a clinical diagnosis over the internet. It sounds like you need a good pediatric neurologist (preferably with a special interest in neuromuscular disease) to evaluate your son's tests. Of course its very important to make the correct diagnosis - this requires careful interpretation of the test and biopsy results

The type of muscle disease that can cause a reaction with anesthesia is called Central Core Myopathy - this is a congenital (present from birth) muscle disease that is very rare and should be diagnosable from the biopsy. Yours son's presentation is not typical for this disease.

Another myopathy or dystrophy may be the cause, and there are a number of different causes. The muscle biopsy is the main way to look for which specific cause as they can all look similar clinically and on EMG. It is important to look for Becker's Muscular Dystrophy (the milder form of Duchenne's, he is probably too old for Duchenne's) by a Dystrophin stain on the muscle biopsy, although the degree of pain is more suggestive of a metabolic myopathy eg muscle enzyme problem. Stains for phosphorylase, phosphofructokinase, and myoadenylate deaminase enzymes should be standard. Other tests can be done on an individual basis depending on the results eg mitochondrial or respiratory transoprt chain enzymes (all enzymes involved in energy metabolism). Other causes like inflammatory myopathies can be seen on the regular microscopic view

Good luck