The 25-year-old Xiao Quan is a veteran, in addition to the occasional cold, fever, no major illnesses. But in the first half of 2008, I do not know why, the whole body just can not make the energy, eating is not as good as before. This condition is becoming more and more obvious. In just a few months, people lost about 10 pounds. Not only that, the fingers gradually feel numb. In desperation, Xiao Quan came to the hospital for examination. Under the doctor’s careful questioning, Xiao Quan mentioned that two years ago, he had the experience of drinking and urinating too much. After a thorough physical examination, the doctor found that Xiaoquan did have a decrease in muscle strength, but that was the extent of it. Some preliminary laboratory tests were then performed. Electromyography showed that motor and sensory nerve conduction in both lower extremities was slowed down, in other words, the sensation and movement of the lower extremities had become “sluggish”. The results of the blood tests were even more surprising. The sodium level in Xiao Quan’s blood was 169 mmol/L, much higher than the normal level (136-145 mmol/L). What does such a high blood sodium level mean for an average person? First of all, it will make a person have a strong need to drink water; secondly, the body will have difficulty tolerating such a high concentration of sodium in the blood, and life is in danger. On the contrary, Xiaoquan had frequent thirst before, but now it does not exist; at the same time, except for weakness and numbness of the limbs and loss of appetite, Xiaoquan has no life-threatening manifestations for the time being. After a scientific analysis of the condition, doctors performed an MRI scan of Xiaoquan’s skull and found a 3×2 cm mass above the structure called the “butterfly saddle”. At this point, the root of Xiaoquan’s disease was found. This is a disease called primary hypernatremia, which is caused by inflammation, tumors, surgery or other lesions in a specific area of the brain. But how do these relatively common diseases trigger rare symptoms? It starts with the regulation of sodium concentration in the blood. Millions of years of species evolution have made the various environments in the human body “optimally designed”. That is, a blood sodium level of 136-145 mmol/L is optimal for survival. Excess or deficiency is harmful to the human body. The role of the brain in regulating blood sodium levels is similar to setting an air conditioner to a standard temperature. We all know that a high or low room temperature needs to be sensed by the air conditioner and then adjusted to run at a constant temperature. Only, the brain’s regulation is more refined and complex. When the blood sodium is too high, the receptors send signals to the brain, so the thirst center produces the feeling of “thirst”. At the same time, the hypothalamus secretes a substance called antidiuretic hormone, which increases the absorption of water by the kidneys and, simply put, reduces the amount of urine excreted. The result of these two regulators is to ensure that more water is available in the body to dilute body fluids. The problem with primary hypernatremia is that the “bar” is set too high. The brain then regulates the level of sodium in the blood according to this faulty setting and determines that the level of sodium is not suitable for human survival as “normal”. But in fact, the high sodium level persists for such a long time that the toxicity to the peripheral nerves is already manifested in the small whole body, i.e., it causes weakness and numbness. Once the mechanism of the disease is understood, it is easier for doctors to take measures to correct the high sodium. For example, forcing the patient to drink water, artificially supplementing with antidiuretic hormone, etc. These are “stopgap” measures. In order to treat the root cause of the disease, it is most important to identify the cause and provide targeted treatment. Primary hypernatremia is not common, but what are the signs that can help us to be aware of it? The most common manifestation of intracranial inflammation and tumor is headache, and once it compresses or invades the adjacent cross structures of the optic nerve, blurred vision will occur. Initially, patients may experience excessive drinking and urination, but as the disease progresses, thirst may be gradually lost or diminished. With longer disease duration, there may be a variety of complex manifestations. The symptoms listed above are not very specific and require specific tests to confirm the diagnosis. Therefore, if you have these problems, it is recommended that you go to an endocrinologist as soon as possible to find the cause.