Lymphocytic pleocytosis

Lymphocytic pleocytosis is an abnormal increase in the amount of lymphocytes in the cerebrospinal fluid (CSF). It is usually considered to be a sign of infection or inflammation within the nervous system, and is encountered in a number of neurological diseases, such as pseudomigraine, Susac's syndrome, and encephalitis. While lymphocytes make up roughly a quarter of all white blood cells (WBC) in the body, they are generally rare in the CSF. Under normal conditions, there are usually less than 5 white blood cells per μL of CSF. In a pleocytic setting, the number of lymphocytes can jump to more than 1,000 cells per μL. Increases in lymphocyte count are often accompanied by an increase in cerebrospinal protein concentrations in addition to pleocytosis of other types of white blood cells. Though exact concentrations differ based on the specific disease, mild cases of lymphocytic pleocytosis are considered to begin when lymphocyte counts enter the range of 10-100 cells per mm3. In healthy individuals, only 0-5 white blood cells per μL are normally present in the CSF. In patients with pseudomigraines, studies have shown concentrations ranging from 10 to 760 cells per mm3, with a mean concentration of 199 ± 174 cells per mm3. Increases in white blood cell count to more than 500 cells per mm3 can cause the CSF to appear cloudy when observed during diagnostic tests. The rise in concentration corresponds to an inflammatory immune response typically seen during viral infections. Despite their diversity, diseases featuring lymphocytic pleocytosis share a number of symptoms, most notably headaches and neurological deficits. Cerebral spinal fluid lymphocytic pleocytosis is generally the result of an immune response to neurovascular inflammation. Many cases point to a viral infection as the root cause of pleocytosis, in which the immune system produces antibodies against neuronal and vascular antigens. This evidence possibly connects it to viral meningitis and Mollaret's disease. Certain non-viral infections, such as Lyme disease have also been considered possible causes.