New Variant of HMPV Virus In China: Will Neurological Symptoms Be The Next Challenge?

In recent years, the rise in cases of autoimmune encephalitis has been closely tied to the detection of neuronal autoantibodies, which are now widely used for clinical diagnosis. As more cases are identified, the reported incidence of autoimmune encephalitis has steadily increased. However, despite this surge, comprehensive epidemiological data on autoimmune encephalitis in both adults and children remains limited, and its characteristics are not yet fully understood.

In southwestern China, particularly in Chongqing, six main types of antibodies have been identified in patients diagnosed with autoimmune encephalitis: anti-NMDA receptor antibody, anti-GABAB receptor antibody, anti-LGI1 antibody, anti-CASPR2 antibody, anti-AMPA1 receptor antibody, and anti-AMPA2 receptor antibody. Between January 2012 and February 2018, 189 patients at six general hospitals tested positive for neuronal autoantibodies. The ongoing investigation into these cases reveals significant variations in disease severity across different age groups and genders. Moreover, researchers are closely examining the relationship between antibody levels and disease severity, hoping to gain further insight into the potential neurological complications associated with these autoimmune responses.

Meanwhile, with the rise in HMP virus cases, especially in China, experts are raising concerns about the virus's ability to trigger neurological symptoms, such as dizziness and cognitive difficulties, which can mirror those seen in autoimmune encephalitis. This connection could be especially crucial as the virus continues to mutate, presenting new challenges in diagnosis and treatment. The recent cases detected in Bengaluru, India, emphasize the need for global monitoring as HMP virus and autoimmune encephalitis could be linked in unexpected ways.

Autoimmune encephalitis (AIE) is one of the most prevalent types of noninfectious encephalitis, primarily caused by an immune system attack on the brain. The condition can be triggered by autoimmune diseases, infections, or even tumors, with some cases being cryptogenic (of unknown origin). AIE typically presents with neurological symptoms that develop rapidly, usually within six weeks. Patients can experience a range of signs, from psychiatric and behavioral changes to movement disorders and seizures.

What Causes Autoimmune Encephalitis?

AIE can result from several autoimmune diseases, including Rasmussen encephalitis, systemic lupus erythematosus (SLE), Behçet's disease, Hashimoto's encephalopathy, and autoimmune limbic encephalitis. These diseases can lead to inflammation in the brain, manifesting in various neurological symptoms. In some cases, AIE is linked to the presence of tumors. The severity of the disease is measured using the Modified Rankin Scale or the Clinical Assessment Scale in Autoimmune Encephalitis (CASE) score, helping doctors track patients' conditions over time.

Symptoms to Watch For

Patients with autoimmune encephalitis may experience a variety of symptoms. Movement disorders such as ataxia (lack of coordination), dystonia (muscle spasms), myoclonus (muscle twitching), and orofacial dyskinesia (abnormal facial movements) are common. Seizures are another hallmark symptom, with some patients experiencing refractory status epilepticus, where seizures are difficult to control. Other symptoms include autonomic disturbances like sweating, rapid heartbeat (tachycardia), high blood pressure (hypertension), and difficulty breathing (hypoventilation). Gastrointestinal issues such as diarrhea and constipation may also occur, alongside sleep disorders like insomnia, sleep apnea, and hypersomnia.

What Happens Inside the Body?

Autoimmune encephalitis occurs when the body's immune system mistakenly attacks healthy neurons, producing antibodies that target neuronal autoantigens. These antibodies are categorized into three types: cell surface antibodies (CSAab), synaptic antibodies (SyAab), and intraneuronal antibodies (INAab), also known as onconeural antibodies. The immune response damages the brain cells, leading to the neurological symptoms associated with AIE.

How Is Autoimmune Encephalitis Diagnosed?

Diagnosing autoimmune encephalitis involves a careful assessment of symptoms and medical history. To meet the criteria for "possible autoimmune encephalitis," patients must exhibit subacute onset (progression within less than three months) of memory issues, altered mental status, or psychiatric symptoms. Additionally, the presence of one or more of the following is necessary:

• New focal central nervous system findings
• Seizures that are not explained by previous conditions
• Cerebrospinal fluid (CSF) pleocytosis, indicating an increase in white blood cells
• MRI scans showing signs of encephalitis

In some cases, doctors may diagnose autoantibody-negative but probable autoimmune encephalitis, where no specific antibodies are found in the blood or CSF. Additional criteria, such as MRI findings or brain biopsy results, are used to confirm the diagnosis and rule out other possible causes.

The classification and severity of autoimmune encephalitis help guide treatment. Typically, treatment focuses on addressing the underlying autoimmune response, often with immunotherapy or other immune-modulating drugs. Symptom management, such as anticonvulsants for seizures or sedatives for agitation, is also important. As the understanding of AIE continues to evolve, earlier diagnosis and improved treatment strategies offer hope for better outcomes for patients suffering from this challenging condition.