Encephalitis

Overview

Encephalitis is a rare and often serious condition characterized by inflammation of the brain. It can be brought on by many causes including viral or bacterial infection, certain medications, or issues with the immune system. 

Autoimmune encephalitis arises when the immune system targets the brain itself, leading to inflammation. Inflammation occurring in the brain due to an infection is referred to as infectious encephalitis, while in some cases, the cause remains unknown.

Common physical manifestations of encephalitis encompass fever, headaches, and neck pain. Encephalitis has the potential to impact brain function, leading to confusion and changes in behavior. Cognitive symptoms of encephalitis may persist long after the resolution of the physical ones. Due to its severity, immediate medical attention is crucial when dealing with encephalitis.

Symptoms

The signs and symptoms of encephalitis can differ from one individual to another and depend on the underlying cause of the inflammation. Encephalitis can manifest with a wide range of symptoms, including but not limited to confusion, changes in personality, seizures, as well as motor and sensory issues, such as changes in vision and hearing.

Typical flu–like and physical symptoms of infectious encephalitis include:

• Fever
• Headache
• Fatigue
• Weakness
• Pain in muscles or joints

Other physical and neurological symptoms that may occur over the course of hours to days include:

• Stiff neck
• Hallucinations, agitation, or confusion 
• Convulsions 
• Unusual movements 
• Loss of sensation or the inability to move specific body or facial parts 
• Muscle weakness
• Speech and hearing issues 
• Sensitivity to light 
• Becoming unconscious, including coma

Signs and symptoms in infants and young children may also include: 

• Poor feedings
• Being irritated
• Vomiting and nausea
• Bulging in the fontanels, the soft areas of a baby’s skull
• Generalized stiffness throughout the entire body.

Everyone experiences different symptoms. However, it is typical for people, especially those with autoimmune encephalitis to experience a mix of symptoms, which may appear over several weeks, more gradually. The symptoms may include:

• Personality changes
• Memory problems
• Seizures
• Hallucinations, hearing, seeing or sensing things that are not present or real
• Psychosis, or the inability to distinguish between what is real and what is not
• Sleep issues
• Changes in vision
• Loss of sensation 
• Weak muscles 
• Walking issues 
• Unusual movement patterns
• Bowel and bladder issues 

If any of the signs and symptoms persist, it is imperative to promptly seek medical assistance. This should be the initial step, even for mild encephalitis symptoms. Additionally, urgent medical attention is essential for infants and young children displaying any signs or symptoms of encephalitis. When an individual experiences a severe headache, high fever, seizures, or alterations in consciousness, it could constitute a medical emergency. Receiving care expeditiously significantly enhances the prospects of a successful recovery.

Causes

The cause determines the type of encephalitis. Although there are several potential causes, the definite cause of encephalitis is unknown in about 50% of its cases. The other half is categorized based on its causes, such as:

• Infectious encephalitis. This condition is typically brought on by viruses. Viral encephalitis is caused by infections with enteroviruses, herpes, HIV, West Nile, and tick–borne viruses. In extremely rare cases, bacteria, fungus, or parasites can cause encephalitis. Infectious encephalitis develops when a virus or other agent directly infects the brain. The illness may just impact a certain area or spread widely.

Viruses that frequently cause encephalitis include:

• • Herpes simplex virus (HSV).  Generally, encephalitis can be induced by both HSV type 1, responsible for cold sores and fever blisters around the mouth, and HSV type 2, which is associated with genital herpes. Encephalitis arising from HSV type 1 can led to severe brain damage or even prove fatal.
  • Other herpes viruses. Encephalitis can be caused by varicella–zoster virus, known for causing chickenpox and shingles, and Epstein–Barr virus, often responsible for infectious mononucleosis.
  • Enteroviruses. Flu–like symptoms, eye inflammation, and abdominal pain are the common symptoms of enteroviruses infection, such as the poliovirus and coxsackievirus.
  • Mosquito–borne viruses. Within a few days to a couple of weeks of being exposed to a mosquito–borne virus, symptoms of an infection may start to show. Viruses carried by mosquitoes have been linked to illnesses including western and eastern equine encephalitis, West Nile, La Crosse, and St. Louis.
  • Tick–borne viruses. The typical onset of symptoms is a week or so following a tick bite. In the Midwestern region of the United States, the Powassan virus, which is spread by ticks, causes encephalitis.
  • Rabies virus. Although possible, encephalitis is rarely caused by rabies. Once symptoms start to appear, rabies infection typically quickly progresses to encephalitis. 
• Autoimmune encephalitis. The immune system may unintentionally target the brain, leading to autoimmune encephalitis. In some, the irregular immune reaction can be induced by noncancerous or cancerous tumors, referred to as paraneoplastic and autoimmune encephalitis. Other types, like acute disseminated encephalomyelitis (ADEM), can be caused by infections in the body, referred to as post–infectious autoimmune encephalitis.

In most cases of autoimmune encephalitis cannot determine the reason or the exact trigger why the immune cells mistakenly attack or produce antibodies against the brain. 

Risk factors

Several factors are known to affect one’s risk of developing encephalitis. This includes:

• Age: Generally, the risk of viral encephalitis is higher in young children and older individuals. In autoimmune encephalitis, some types are more prevalent in children and young adults while others are more prevalent in elderly people. 
• Compromised immune system: Encephalitis is more likely to develop among those with HIV/AIDS, those who take immune–suppressing medications, and those who have another illness that compromises immunity.
• Autoimmune disease: Autoimmune encephalitis may be more likely to occur in people who already have an autoimmune disease.
• Geographical location: In some areas of the world, viruses spread by ticks or mosquitoes are prevalent.
• Season of the year: In many parts of the United States, diseases spread by ticks and mosquitoes are more prevalent in the summer.
• Smoking: Smoking elevates the likelihood of developing lung cancer, subsequently raising the risk of paraneoplastic autoimmune encephalitis.