Some people (not scientists) say that we only use half of our brain. While this sounds impressive, I'm not sure what it means - it certainly goes against what I learned in neurology. Nonetheless, it can be surprising to see just how much disruption this soft, watery organ can withstand.
Our patient is a young, HIV-positive man. Like so many of the HIV patients I've seen here, he isn't on any anti-retrovirals. He's come in to the hospital because of three weeks' headaches, which are getting worse. He's also got a fever, and has vomitted on a few occasions. There's no neck stiffness, no lymph nodes and neurologically he's intact. In fact, looking at him, there's very little to suggest anything's wrong. He is well enough to face the ambulance trip across Ho Chi Minh City to the nearest MRI centre: cue sirens and unnecessarily hazardous driving.
As medical students, when reading scans, we're always taught to start by checking the identity of the patient. It would be tempting to assume that the MRI which has just been put up on the light box is of a different patient, but it isn't. The left half of his brain is distorted by a large, ring-enhancing lesion surrounded by oedema. A smaller lesion lies in the occipital lobe. It is hard to believe that this is the brain of the young man who was talking to us earlier and later went out for a walk.
While TB and primary CNS lymphoma are possibilites here, this is toxoplasmosis. The intracellular protozoan parasite Toxoplasma gondii probably infected our patient many years ago, before he had AIDS. His immune system controlled the infection but parasite cysts remained dormant in his muscles and other organs. As a result of HIV, Toxoplasma became reactivated and invaded his brain in dramatic fashion.
About 20% of the world's population has been infected with Toxoplasma, usually as a result of eating under-cooked meat. Our fluffy feline friends are the main hosts for the parasite, innocently fertilising gardens and fields with it. Farm animals then eat it, or we forget to wash our hands, and thus become infected. While most people will experience only a flu-like illness, foetuses can die from toxoplasmosis, which is why pregnant women have to be particularly careful when cooking meat.
As with many parasitic diseases, humans are just an accidental host in the organism's life-cycle, and one which doesn't do it any good. But as our patient demonstrates, such accidents can have devastating effects on vulnerable patients. Fortunately, six weeks' antimicrobials will restore his brain's integrity and he will soon be back to normal. Well, as normal as can be with untreated AIDS.
Our patient is a young, HIV-positive man. Like so many of the HIV patients I've seen here, he isn't on any anti-retrovirals. He's come in to the hospital because of three weeks' headaches, which are getting worse. He's also got a fever, and has vomitted on a few occasions. There's no neck stiffness, no lymph nodes and neurologically he's intact. In fact, looking at him, there's very little to suggest anything's wrong. He is well enough to face the ambulance trip across Ho Chi Minh City to the nearest MRI centre: cue sirens and unnecessarily hazardous driving.
As medical students, when reading scans, we're always taught to start by checking the identity of the patient. It would be tempting to assume that the MRI which has just been put up on the light box is of a different patient, but it isn't. The left half of his brain is distorted by a large, ring-enhancing lesion surrounded by oedema. A smaller lesion lies in the occipital lobe. It is hard to believe that this is the brain of the young man who was talking to us earlier and later went out for a walk.
While TB and primary CNS lymphoma are possibilites here, this is toxoplasmosis. The intracellular protozoan parasite Toxoplasma gondii probably infected our patient many years ago, before he had AIDS. His immune system controlled the infection but parasite cysts remained dormant in his muscles and other organs. As a result of HIV, Toxoplasma became reactivated and invaded his brain in dramatic fashion.
About 20% of the world's population has been infected with Toxoplasma, usually as a result of eating under-cooked meat. Our fluffy feline friends are the main hosts for the parasite, innocently fertilising gardens and fields with it. Farm animals then eat it, or we forget to wash our hands, and thus become infected. While most people will experience only a flu-like illness, foetuses can die from toxoplasmosis, which is why pregnant women have to be particularly careful when cooking meat.
As with many parasitic diseases, humans are just an accidental host in the organism's life-cycle, and one which doesn't do it any good. But as our patient demonstrates, such accidents can have devastating effects on vulnerable patients. Fortunately, six weeks' antimicrobials will restore his brain's integrity and he will soon be back to normal. Well, as normal as can be with untreated AIDS.
