General analysis of cerebrospinal fluid

A general analysis of cerebrospinal fluid includes counting the number and composition of blood cells. Normally, 1 μl of cerebrospinal fluid contains 4-6 cells (lymphocytes). In pathological processes (inflammation of the brain envelopes, encephalitis, volumetric processes, acute insufficiency of cerebral circulation), the number of cellular elements increases. With purulent meningitis in the cerebrospinal fluid, neutrophils appear in large numbers (up to several tens of thousands in 1 μl), with serous meningitis the number of cells increases from a few tens to 1-2 thousand due to lymphocytes. The ratio of neutrophils and lymphocytes (cytogram) is calculated as a percentage. Often, the number of red blood cells is detected and counted. In addition, spinal fluid can detect eosinophils (with parasitic diseases of the central nervous system), macrophages (with prolonged inflammatory processes), atypical cells (with tumors of the brain membranes, leukemia). When suspected of having atypical cells, a smear of cerebrospinal fluid is examined by a cytologist. Calculation of the cytosis and cytograms has not only diagnostic value, but also allows to evaluate the effectiveness of antibacterial therapy in bacterial meningitis.

As additional tests, cytochemical methods are used that allow one to judge the functional state of cells of cerebrospinal fluid (determination of glycogen content and activity of neutrophil myelopyroxidase, activity of lymphocytes, etc.).

Counting cells in the cerebrospinal fluid is desirable to be performed within 1-2 hours after the puncture. In later terms, the cellular composition can significantly change due to cell lysis, precipitation and the formation of fibrin clots. Since erythrocytes in the cerebrospinal fluid are rapidly lysed, they are determined only by the presence of fresh blood in the subshell space: after traumatic punctures, subarachnoid hemorrhages, parenchymal hemorrhages with penetration of erythrocytes into the cerebrospinal fluid, venous thrombotic occlusions with vein swelling and secondary diffusion of blood cells through the venous wall .

The upper limit of the normal number of leukocytes in the cerebrospinal fluid is 5 in 1 μl. However, some syphilologists consider the upper index of the norm to be not 5, but 9 cells. A small pleocytosis up to 20 in 1 μl is usually observed after pyelography, spinal anesthesia, cerebral stroke. Incomparably more severe changes are noted in infectious diseases of the central nervous system. Acute bacterial meningitis is usually accompanied by much more pronounced pleocytosis than meningitis aseptic. Thus, with the majority of bacterial meningitis there is pleocytosis of more than 1000 in 1 μl; However, in the early stages or in the case of partially treated meningitis (!), pleocytosis may be less. In aseptic meningitis, such a high pleocytosis is rare. In cases where pleocytosis is particularly large (5000-10000 in 1 μl), in addition to meningitis, a rupture of the intracerebral or peri-meninge abscess can be suspected; while a lightning-fast increase in clinical symptoms is usually observed. Usually an increase in the concentration of polymorphonuclear leukocytes is observed in bacterial meningitis. Elevated levels of lymphocytes are usually observed with chronic infections (tuberculosis and fungal meningitis), untreated bacterial infections, viral infections, non-infectious inflammatory processes (eg, exacerbation of multiple sclerosis). Eosinophilia is rare and indicates helminthiasis, including cysticercosis, and is also observed sometimes in tuberculous meningitis, CNS lymphomas and foreign bodies.

Immunological methods

Methods based on the determination of the pathogen antigens and antibodies are used. The most commonly used method of RLS for the detection of antigens of meningococcus, pneumococcus and hemophilic rod type b. For the diagnosis of tuberculosis meningitis, immunoenzymatic analysis (ELISA) is used, if suspected of herpes encephalitis, specific antibodies in the cerebrospinal fluid are determined.

Polymerase chain reaction (PCR) is widely introduced into practice, as it allows to identify the vast majority of neuroinfectious pathogens and in practical conditions to establish the etiology of neuroinfections in 90% of patients. Advantages of the method are high sensitivity and specificity, the ability to detect fragments of the genome of the pathogen against the background of treatment, to determine if necessary microbial load. To reduce costs, it is recommended initially to react with primers of common pathogens (meningococcus, pneumococcus, haemophilus b type, enteroviruses), and then with more rare pathogens (gram-negative bacteria, borrelia, mycobacterium tuberculosis, herpetic viruses, viruses, agents of children's drip infections, etc. .). The picture of cerebrospinal fluid depends on the timing of the study and the treatment.

Cytological examination of cerebrospinal fluid makes it possible to sometimes identify atypical cells present even in minimal amounts. This is an important method for detecting CNS tumor lesions.

Inflammatory processes accompanied by leukocytosis may also have certain cytological characteristics. So, the lymphocytes appearing in the cerebrospinal fluid in response to a viral infection can have clearly visible nuclei, because of which they are sometimes confused with malignant cells. Herpetic encephalitis may be accompanied by the appearance of large intranuclear inclusions in lymphocytes or ependymocytes; such a finding is pathognomonic. In cryptococcal infections, yeast-like colonies can be detected either in the free state or intracellularly in macrophages. Subarachnoid hemorrhage leads to the appearance of macrophages (erythrophages), stretched by multiple vacuoles. Macrophages are initially filled with red blood cells and lipid products of their decay, and subsequently - hemosiderin. In some accumulation diseases, such as the Tay-Sachs disease, macrophages with a foamy cytoplasm, filled with the products of the decomposition of ganglion cells, are identified. The identification of tumor cells is based on the identification of a number of cytological features characteristic of the neoplastic process. The reliability of the cytological diagnosis of a tumor is greater, the more neoplastic features are revealed. More often, cytologic studies of cerebrospinal fluid are used to diagnose lesions of CNS in acute leukemia and lymphomas, which are usually disseminated into the subarachnoid space. Special antibodies against B- and T-lymphocytes are used for immunodiagnostics. Thus, in general inflammatory processes, T lymphocytes predominate, and in malignant processes, the predominant proliferation of pathological clones of B lymphocytes is observed. Immunohistochemical studies are used to identify the specific form of leukemia. It should, however, be borne in mind that with leukemia accompanied by the release of pathological cells into the bloodstream, the results of the study of cerebrospinal fluid can be false-positive due to the entry of these cells with ground blood. It is important to remember that the cytological examination of cerebrospinal fluid is effective only in those malignant processes in which the membranes of the brain are involved. Carcinomatosis of meninges often occurs when metastasizing cancer of the lung, breast, abdomen and melanoma.

[1], [2], [3], [4]