Flushing the kidneys
Whatever the cause, she told the worried young man that his muscles would be recovering. But his kidneys were in danger. His urine was dark because the oxygen-carrying parts of the muscle known as myoglobin built up in the kidneys. Myoglobin is a dark red color; That is why the muscle is red. The most important thing the medical team did for him at that moment was to give him fluids to help his kidneys flush out myoglobin and other components released by the damaged muscle.
Ue ordered additional tests to track the patient’s creatine kinase. At the time of admission, his total CK, which was originally stated to be over 40,000, was actually 189,000. It almost doubled the next day: 364,000. Ue kept the fluids going, looking for a reason for the worst case of rhabdo she had ever seen. It wasn’t hepatitis or any of the common viruses they were tested for. It wasn’t Wilson’s disease. It wasn’t one of the drugs she was looking for.
A fuel problem?
What else? Looking for an answer, she turned to the medical literature and found a paper describing two young people who, like her patient, developed severe rhabdo after moderate exercise. The authors listed factors that could predispose a patient to this type of muscle injury and Ue found what she was looking for. There are people born with abnormalities in the way their bodies use the fuel provided by the food they eat. Because of this anomaly, these people could literally run out of fuel during stress or hard work. Could he have one of these rare hereditary diseases? To answer this question, after the patient recovered enough to leave the hospital, Ue referred him to a neurologist who specializes in neuromuscular disorders.
Months later, the patient had enough time to make an appointment with Dr. Courtney McIlduff, a neurologist at Beth Israel Deaconess Medical Center in Boston. Since his week in the hospital, the man reported, he has had two more episodes – albeit not as severe as the first. Both happened after taking an easy walk. Upon hearing this, McIlduff, like Ue, began to ponder an inherited problem with converting food into fuel. These so-called metabolic myopathies sometimes only show up in adolescence or even adulthood.
McIlduff examined the man carefully, looking for muscle weakness. Many forms of muscle disorders can permanently change the look or function of muscles, but most metabolic myopathies cannot. The patient’s muscle examination was completely normal. She sent him for genetic testing to look for one of the many inherited metabolic disorders.
And indeed, he had one: he was born without the ability to make an enzyme called carnitine palmitoyl transferase type 2. Patients with CPT2 deficiency lack the necessary biological equipment to convert some dietary fats into energy. Usually the body runs on a type of sugar made up of carbohydrates that is stored in the liver. When this sugar is used up, the body switches to fat for fuel. Patients with CPT2 deficiency cannot do this, or at least not well. Without the proper fuel, the muscle cells will be injured and release their contents, causing pain and dark urine. Neither of the man’s parents has this disorder, but both have a copy of the faulty gene for this enzyme. It takes two copies to get the disease, so your son got one copy of each of them.
