Late Diagnosis of Adult-Onset Carnitine Palmitoyltransferase II Deficiency in a 63-Year-Old Man Presenting with Recurrent Rhabdomyolysis: A Case Report

The Body's Fuel Switch: A Story of Stuck Engines

Imagine your body is a high-performance car. To keep the engine running, it needs fuel. For quick bursts of speed, it burns sugar (glucose), which is easy to grab. But for long road trips, like running a marathon or just surviving a night without eating, the car switches to a different fuel tank: fat. Fat is a super-dense energy source, but it's tricky to use. It can't just drive straight into the engine's combustion chamber (the mitochondria); it needs a special delivery truck to get it inside.

This delivery truck is called the "carnitine shuttle." It picks up fat molecules and ferries them across a gate into the engine room. Once inside, the fat is burned to create power. However, there's a critical part of this truck system called the "CPT II" enzyme. Think of CPT II as the unloading dock at the engine door. Its job is to take the fat off the truck and drop it onto the conveyor belt so it can be burned. If this unloading dock is broken, the fat trucks pile up outside the door, the engine runs out of power, and the whole system starts to sputter and break down. This is what happens in a condition called CPT II deficiency. It's a rare genetic glitch where the body struggles to turn fat into energy, leading to muscle pain and damage, especially when the body is stressed by exercise or hunger.

The Case of the 63-Year-Old Mystery

This paper tells the story of a 63-year-old man who had been living with a confusing medical mystery for over a decade. Since 2011, he had been visiting doctors repeatedly because of severe muscle pain, weakness, and dark, cola-colored urine. These symptoms were signs of rhabdomyolysis, a condition where muscle fibers break down and leak into the bloodstream. For years, doctors thought he had myositis (an inflammation of the muscles caused by the immune system attacking the body). They ran tests, gave him treatments, and watched him get better and worse again and again.

But something didn't add up. Every time he got better, his muscles seemed fine, and his nerve tests were normal. Yet, his blood tests showed a persistent, high level of creatine kinase (CK), a chemical that leaks out of damaged muscles. In fact, during his latest hospital visit, his CK level was a staggering 6,292 U/L. The doctors also checked his blood for autoimmune diseases (like lupus or rheumatoid arthritis) and found nothing; all his immune system markers were negative. He wasn't taking any drugs that usually hurt muscles, and he hadn't been in a car accident.

The doctors realized that if his immune system wasn't attacking him, and his nerves were fine, maybe the problem was how his muscles were making energy. They suspected a "metabolic myopathy"—a problem with the body's fuel processing. To solve the puzzle, they looked at his DNA.

The Genetic "Smoking Gun"

The team ran a comprehensive genetic test, looking at a panel of genes known to cause muscle diseases. They found the answer: a specific, broken instruction in the CPT2 gene. The patient had two copies of a mutation called c.338C > T (p.Ser113Leu).

To put it simply, this mutation is a typo in the instruction manual for building the "unloading dock" (the CPT II enzyme). Because of this typo, the dock doesn't work properly. The patient's body couldn't move long-chain fats into the mitochondria to be burned for energy. When he exercised or went without food, his muscles ran out of fuel, broke down, and caused the rhabdomyolysis attacks.

This discovery was a big deal because the patient was 63 years old. Usually, this type of genetic error is spotted in teenagers or young adults. The fact that he had been misdiagnosed with "myositis" for over 12 years shows how tricky this condition can be. The paper notes that a muscle biopsy taken years earlier had been misread as "myositis," likely because the muscle looked inflamed due to the damage, not because the immune system was attacking it. The paper argues that this misinterpretation, combined with the lack of a family history of the disease, caused the long delay in diagnosis.

What This Means for the Patient

Once the diagnosis was confirmed, the treatment plan changed completely. Instead of trying to suppress an immune system that wasn't the problem, the doctors focused on managing the fuel supply. The patient was advised to:

• Avoid prolonged fasting: Don't let the body run out of sugar before it can switch to fat.
• Avoid strenuous exercise: Don't push the engine past its breaking point.
• Follow a specific diet: A low-fat, high-carbohydrate diet to keep the sugar fuel tank full.

The paper concludes that this case is a warning to doctors: if an adult has recurrent muscle breakdown, high CK levels, and normal nerve tests, don't just assume it's an autoimmune disease or a random injury. It could be a metabolic fuel problem like CPT II deficiency, even if the patient is in their 60s. Catching it early through genetic testing can stop the cycle of pain and prevent unnecessary, invasive procedures.