Diagnosis of meningitis
Acute meningitis is a serious disease requiring emergency diagnosis and treatment. The first urgent diagnostic measures are blood sowing for sterility, as well as lumbar puncture followed by bacteriological study of cerebrospinal fluid (Gram staining and culture), biochemical analysis including determination of protein and glucose level, and cytological examination with differentiated cell counting. If the patient has symptoms of intracranial volumetric process (focal neurological deficit, congestive discs of optic nerves, impaired consciousness, epileptic seizures), before performing a lumbar puncture, CT should be done to exclude the possibility of wedging in the presence of an abscess or other voluminous formation.
The results of the analysis of cerebrospinal fluid can help in the diagnosis of meningitis. The presence of bacteria in a stained smear or the growth of bacteria in the seed is the basis for the formulation of the diagnosis of bacterial meningitis. In the Gram stain smear of the cerebrospinal fluid, about 80% of the cases are detected by bacteria, which are often identified already at this stage of the study. Lymphocytosis and the absence of pathogens in CSF testify to the use of aseptic meningitis, although they can also occur in the treatment of bacterial meningitis.
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Analysis of cerebrospinal fluid with meningitis
For the diagnosis of meningitis of any etiology, a lumbar puncture with CMC smear microscopy, study of protein and sugar concentration, seeding and other diagnostic methods is mandatory.
CSF pressure usually does not exceed 400 mm of water column. Viral meningitis is characterized by lymphocytic pleocytosis within 10-500 cells, in some cases the number of cells can reach several thousand. Neutrophils at the onset of the disease (6-48 h) may be more than 50% of the cells, in this case, some experts recommend repeating the lumbar puncture after 5-8 h to see if the nature of the cytosis changes. The protein concentration is moderately elevated (less than 100 mmol / l). The glucose level is usually about 40% of the blood level.
CSF pressure usually exceeds 400-600 mm of water column. Characteristic is the predominance of neutrophils with a cytosis of 1000-5000 cells in 1 μl, sometimes more than 10,000. In approximately 10% of patients at the onset of the disease, the cytosis can be predominantly lymphocytic, more often in neonates with meningitis caused by L monocytogenes (up to 30% of cases) with low cytosis and a large number of bacteria in the CSF. Approximately 4% of patients with bacterial meningitis have cytosis in the CSF, usually they are newborns (up to 15% of cases) or children up to 4 weeks (17% of cases). Therefore, all CSF specimens should necessarily be stained with Gram, even in the absence of cytosis. Approximately 60% of patients show a decrease in the concentration of glucose in the CSF (<2.2 mmol / l) and a ratio of blood glucose and in the CSF below 31 (70% of patients). The concentration of protein in CSF increases in virtually all patients (> 0.33 mmol / L), this is considered a differential diagnostic feature with non-bacterial meningitis in patients who have not previously received antibiotics.
The staining of CSF smears by Gram is considered to be a quick and accurate method of detecting pathogens in 60-90% of cases of bacterial meningitis, the specificity of the method reaches 100%, correlates with the concentration of specific bacterial antigens and bacteria. At a bacterial concentration of 103 cfu / ml, the probability of detecting bacteria using Gram staining is 25%, at a concentration of 105 and higher, 97%. The concentration of bacteria may decrease in patients who have already received antibiotics (up to 40-60% if detected by staining and below 50% by sowing). It was shown that in neonates and children with bacterial meningitis and the isolation of bacteria from a CSF sample obtained during a diagnostic spinal puncture, the restoration of CSF sterility in 90-100% occurred within 24-36 hours after the onset of adequate antibacterial therapy.
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With meningitis caused by candidiasis, pleocytosis averages 600 cells per 1 μl, the nature of pleocytosis can be both lymphocytic and neutrophilic. In microscopy, fungal cells are found in about 50% of cases. In most cases, it is possible to obtain fungal growth from CSF. In meningitis caused by cryptococci, CSF usually has low pleocytosis (20-500 cells), in 50% there is neutrophilic pleocytosis, the protein concentration is increased to 1000 mg% or more, which may indicate a block of subarachnoid space. For the detection of fungi a special staining is used, which allows obtaining positive results in 50-75%. With meningitis caused by coccidia, note eosinophilic pleocytosis, the causative agent is isolated in 25-50% of cases.
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Etiological diagnosis of meningitis
With the development of methods of molecular diagnostics (PCR), the effectiveness of diagnostics of viral infections of the central nervous system has significantly increased. This method reveals conserved (characteristic for this virus) areas of DNA or RNA, has a high sensitivity and specificity in the study of normally sterile media. This method almost supplanted virological and serological diagnostic methods due to high efficiency and rapidity (the study continues <24 h).
There are several methods for confirming the etiology of meningitis:
- Counter immunophoresis (the duration of the study is about 24 hours) allows the detection of antigens of N. Meningitidis, H. Influenzae, S. Pneumoniae, group B streptococci, E. Coli. The sensitivity of the method is 50-95%, the specificity is more than 75% - it allows to identify the antigens of N. Meningitidis, H. Influenzae, S. Pneumoniae, group B streptococci, E. Coli.
- Latex agglutination (duration of the test less than 15 min) allows to detect antigens of N. Meningitidis, H. Influenzae, S. Pneumoniae, group B streptococcus, E. Coli.
- PCR diagnosis (duration of the study less than 24 hours) allows to detect the DNA of N. Meningitidis and L. Monocytogenes, the sensitivity of the method is 97%, the specificity is about 100%.
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Radiation diagnosis of meningitis
Skull examination using a computer and MRI is not used to diagnose meningitis. However, these methods are widely used to diagnose the complications of this disease. An unusually long period of fever, clinical signs of high ICP, the appearance of persistent local neurological symptoms or seizures, an increase in head size (newborns), the presence of neurological disorders, and the unusual duration of the CSF sanation process are considered indications for use. These studies are very effective for diagnosing liquorrhea in patients with meningitis due to fracture of the base of the skull, detection of fluid accumulation in the skull and accessory sinuses of the nose.