Viral meningitis overview

# Overview
Viral meningitis is a condition in which the layers lining the brain, or meninges, become inflamed due to a viral infection. Meningitis is diagnosed on a history of characteristic symptoms and certain examination findings (e.g. Kernig's sign). Investigations should show an increase in the number of leukocytes present in the cerebrospinal fluid (CSF), obtained via lumbar puncture.

# Historical Perspective
Meningitis was first discovered by Hippocrates. Wallgren described aseptic meningitis in 1924 and defined it as a disease with acute onset that had typical systematic symptoms of meningeal involvement, in association with a cerebrospinal fluid (CSF) typical of meningitis (typically with a mononuclear cell predominance). Additionally, there was absence of bacteria on stain and culture and there was no identifiable parameningeal infection.

# Classification
There is no specific classification to the viral meningitis. However, it may be classified based on the age into child and adult viral meningitis. It may be also according to the causative virus like enterovirus, arbovirus, mumps and herpes simplex viruses.

# Pathophysiology
Viral meningitis pathophysiology may differ from virus to another and depends on many factors like age, immune status and gene expression. Invasion into the meninges by a pathogen can set up a local inflammatory response. The clinical signs are due to this meningeal irritation. Kernig's sign is due to pain produced by stretching of the inflamed meninges.

# Causes
Viral meningitis is caused by many viruses. The most important and the most common virus group that causes meningitis is Enteroviruses group. There are other viruses cause meningitis as arbovirus and herpes simplex virus groups but not common as the enteroviruses.

# Differential diagnosis
The differential diagnosis of viral meningitis includes two step approach. First is differentiating viral meningitis from other diseases which have similar clinical presentation as viral meningitis such as encephalitis, brain abscess, subarachnoid hemorrhage, and brain tumour. Second step involves CSF examination and differentiating viral meningitis from bacterial, fungal and other causes of meningitis

# Epidemiology and demographics
Viral meningitis affect around 26,000 to 42,000 individual annualy with incidence 11 per 100,000 population. There is no gender or racial predilection.

# Risk Factors
Viral meningitis risk factors rely particularly on the exposure to the infection itself and the route of transmission like respiratory droplet and feco-oral transmission. However, there are people at risk to be infected by the disease as children less than 5 years and immunocompromised patients.

# Natural History, Complications and Prognosis
Viral meningitis is a self resolved disease if left untreated. It takes around 10 days to be resolved. Seizures and loss of consciousness are the most important complications that may appear in the infants younger than 3 months. It has an excellent prognosis.

# Diagnosis

## History and symptoms
Viral meningitis symptoms are varied, depending on the causative organism.  The symptoms of viral meningitis usually last from 7 to 10 days, and people with normal immune systems usually recover completely. A rash may be present, which could suggest a particular virus e.g. varicella zoster. However, a non-blanching purpuric rash is not associated with meningitis and suggests systemic bacterial infection.
The more common symptoms of meningitis are fever, severe headache, stiff neck, bright lights hurting the eyes, drowsiness or confusion, and nausea and vomiting. In babies, the symptoms are more difficult to identify. They may include fever, irritability, difficulty in awakening the baby, or the baby refuses to eat. The symptoms of meningitis may not be the same for every person.

## Physical examination
Viral meningitis patients appear lethargic and may be not well oriented. They also appears feverish grading (40C/104F). The signs may differ according to the patient age and the virus causing the disease as well. Different signs can be noticed like photophobia, phonophobia, nuchal rigidity, altered mental status, and skin rash.

## Laboratory findings
Viral meningitis lab tests include non specific blood tests like the CBC, blood culture, PT and PTT tests. Other tests include some tissues swabbing like the throat and nose swab to detect the viruses. PCR is also recommended for virus detection. CSF studies is the most important specific diagnostic test for the viral meningitis and it also differs between the various types of meningitis.

## CT scan
Viral meningitis diagnosis depends on mainly the CSF studies. CT scan is required for imaging before applying the lumbar puncture to see if there is any contraindication for the procedure. However, CT scan may be performed to exclude other brain diseases that can be misinterpreted with the viral meningitis.

## MRI
Viral meningitis diagnosis depends on mainly the CSF studies.However, MRI scan may be performed to exclude other brain diseases that can be misinterpreted with the viral meningitis.

## Ultrasound
There are no ultrasound findings associated with viral meningitis.

## Xray
There are no x-ray findings associated with viral meningitis.

## Other imaging findings
There is no other imaging findings to diagnose the viral meningitis.

## Other diagnostic studies
There is no other diagnostic studies for the viral meningitis.

# Treatment

## Medical therapy
Viral meningitis has no specific treatment as most of the patients recover within 7-10 days. General supportive measures are recommended to manage the cases and prevent proceeding to serious conditions like the brain edema. These measures include: analgesics for the pain, acetaminophen for the fever and electrolytes management  However, antiviral medical therapy can be provided for the patients caused with specific viruses like the enteroviruses or the influenza. In severe cases, the patients will need to be hospitalized.

## Surgery
Surgical intervention has no role in the management of viral meningitis.

## Prevention
Primary prevention of viral meningitis depends mainly on the self hygiene and some measures that should be considered like: washing hands regularly, avoid touching face, avoid close contact with suspected individuals, and staying home when feeling sick. There are no vaccines against the enteroviruses but other viruses like influenza should be vaccinated to prevent the development of the disease. There is no secondary prevention for viral meningitis.