Salt

Salt is a mysterious substance. If we take in too much, our kidneys suffer and our blood pressure goes up. However, I recently had a mysterious case of the opposite problem. A highly functioning executive is brought in by her neighbor because she has been acting strange. For the last few weeks to months, she has been falling quite a bit, to the point that she has multiple rib fractures of varying ages, a bleed within her head, and bruises all along her arms and legs. She also has lapses in her memory and can't give us a good history. She lives alone, and there is no real suspect for violence or abuse. Her vital signs are stable but she's pretty confused; she can't even tell me the month or year.

Usually, patients like this don't come to the medical intensive care unit. If trauma is a big factor, they may go to the surgical trauma service; otherwise, general internal medicine or neurology wards should be sufficient to stabilize the patient and figure things out. I was called, however, because of a surprising lab finding. Her sodium level was 110; normal is 135-145. This is probably the lowest sodium I've ever seen, and it's life threatening. With so little salt in her body, she was at risk for seizures and coma.

Every medical student learns the differential diagnosis - possible causes - of low sodium or hyponatremia. However, it was not so easy figuring her out. She had no evidence of heart failure, kidney failure, or cirrhosis. She didn't have profound bleeding or diarrhea or volume loss. We began looking for occult cancers, thyroid problems, adrenal insufficiency. We began wondering about her diet, though she didn't appear to have severe malnutrition.

Over the next few hours, the story became stranger and stranger. Normally, when someone has low salt, the body conserves water by producing less urine. However, she was peeing up a storm. This suggested that she was driving her salt levels down by drinking profound amounts of water. It takes an unbelievable amount of water to bring one's sodium down to 110; in fact, most of the time we see this condition (primary polydipsia), it is due to psychiatric illness. Sometimes, the mental illness is so severe that patients will drink from a toilet to get that water. We still don't know why she has primary polydipsia.

Meanwhile, she develops a fever. She is given antibiotics in the emergency department, and she develops a profound rash. Her labs then show a dropping platelet count, so severe that we can't even do a spinal tap for her. Lastly, scans performed in the emergency department raise the possibility of an incredibly rare cancer, carcinoid tumor.

From time to time, we do, of course, run into medical mysteries. We have the infection we cannot trace, the bleed we cannot locate, the cause of liver disease we cannot identify. But a case this bizarre I haven't had in a while. Overnight, we stabilized her and began the diagnostic battery, but we shall see if answers turn up in the next few days.

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