Subacute sclerosing panencephalitis

Subacute Sclerosing Panencephalitis (SSPE), also known as Dawson Disease, is a rare and devastating neurological disorder characterized by chronic progressive brain inflammation. This condition is caused by slow infection with certain defective strains of hypermutated measles virus. SSPE primarily affects children, teenagers, and young adults, with an estimated incidence of about 1 in 10,000 individuals who contract measles. In this comprehensive article, we will explore the definition, causes, clinical features, diagnosis, treatment, and implications of SSPE.

Understanding SSPE

Subacute Sclerosing Panencephalitis is a rare but severe complication of a prior measles infection. It is caused by the persistence of measles virus within the central nervous system.

Causes and Pathogenesis

The underlying cause of SSPE is believed to be the presence of defective and mutated measles virus particles within the brain. These altered viral particles can persist for years after the initial measles infection and gradually lead to neurological damage.

Signs and symptoms

SSPE is characterized by a history of primary measles infection, followed by an asymptomatic period that lasts 7 years on average but can range from 1 month to 27 years. After the asymptomatic period, progressive neurological deterioration occurs, characterized by behavior change, intellectual problems, myoclonic seizures, blindness, ataxia, and eventually death.

Progression

Symptoms progress through the following 4 stages:

• Stage 1: There may be personality changes, mood swings, or depression. Fever and headache may also be present. This stage may last up to 6 months.
• Stage 2: This stage may involve jerking, muscle spasms, seizures, loss of vision, and dementia.
• Stage 3: Jerking movements are replaced by writhing (twisting) movements and rigidity. At this stage complications may result in death.
• Stage 4: The final stage, in which breathing, heart rate, and blood pressure are affected, leading to coma and death.

Pathogenesis

A large number of nucleocapsids are produced in the neurons and the glial cells. In these cells the viral genes that encode envelope proteins have restricted expression. As a result, infectious particles like the M protein are not produced, and the virus is able to survive persistently without evoking an immune response. Eventually the infection will lead to SSPE.

Diagnosis

According to the Merck Manual:

"SSPE is suspected in young patients with dementia and neuromuscular irritability. EEG, CT or MRI, CSF examination, and measles serologic testing are done. EEG shows periodic complexes with high-voltage diphasic waves occurring synchronously throughout the recording. CT or MRI may show cortical atrophy or white matter lesions. CSF examination usually reveals normal pressure, cell count, and total protein content; however, CSF globulin is almost always elevated, constituting up to 20 to 60% of CSF protein. Serum and CSF contain elevated levels of measles virus antibodies. Anti-measles IgG appears to increase as the disease progresses. If test results are inconclusive, brain biopsy may be needed."

Treatment

If the diagnosis is made during stage 1 it may be possible to treat the disease with oral isoprinosine (Inosiplex) and intraventricular interferon alfa, but the response to these drugs varies from patient to patient, and the only accepted treatments are supportive measures such as anticonvulsants.

Prognosis

In the classic presentation of the disease death occurs in 1 to 3 years, but faster and slower progressions can occur. Faster deterioration in cases of acute fulminant SSPE leads to death within 3 months of diagnosis.

Although the prognosis is bleak for SSPE past stage 1, there is a 5% spontaneous remission rate—this may be either a full remission that may last many years or an improvement in condition giving a longer progression period or at least a longer period with the less severe symptoms.

Epidemiology

SSPE is a rare condition, although there is still relatively high incidence in Asia and the Middle East. However, the number of reported cases is declining since the introduction of the measles vaccine—eradication of the measles virus prevents the SSPE mutation and therefore the progression of the disease or even the initial infection itself.

Epidemiology

SSPE is a rare condition, and its incidence varies by region and vaccination rates. In areas with high measles vaccination coverage, the occurrence of SSPE is significantly reduced.

Clinical Presentation

The clinical presentation of SSPE is characterized by progressive and debilitating neurological symptoms, including:

Cognitive Decline

Patients with SSPE often experience a decline in cognitive function, including memory loss, personality changes, and impaired intellectual abilities.

Muscle Spasticity

Muscle spasticity, characterized by muscle stiffness and involuntary contractions, is a common symptom of SSPE.

Seizures

Seizures are a frequent manifestation of SSPE and can vary in severity.

Visual Disturbances

Patients may experience visual disturbances, including blindness, due to damage to the optic nerve.

Diagnosis and Assessment

Diagnosing SSPE is based on a combination of clinical symptoms, medical history, and diagnostic tests, including cerebrospinal fluid analysis, electroencephalography (EEG), and neuroimaging.

Treatment and Management

There is no cure for SSPE, and treatment primarily focuses on symptom management and supportive care. Antiviral medications may be administered in an attempt to slow the progression of the disease, but their effectiveness is limited.

Prognosis and Implications

SSPE is a progressive and fatal disease, with a poor prognosis. The disease typically leads to severe disability and ultimately results in death. The course of the disease can vary, but it is universally devastating for affected individuals and their families.

Prevention

The most effective way to prevent SSPE is through measles vaccination. High vaccination rates contribute to herd immunity, reducing the incidence of measles and, consequently, SSPE.

World Health Organization (WHO): Background Paper on Subacute Sclerosing Panencephalitis (SSPE) - Detailed report on SSPE and its association with measles.

Conclusion

Subacute Sclerosing Panencephalitis (SSPE) is a rare but devastating neurological disorder resulting from persistent measles infection within the central nervous system. While it is a rare complication of measles, its profound impact on cognitive and motor function underscores the importance of measles vaccination. Understanding the clinical features, diagnosis, and implications of SSPE is essential for healthcare professionals and public health efforts aimed at preventing this tragic condition.

For more information on related topics, please explore our Measles and Neurological Disorders articles.

References

1. Gadoth, N., & Ravid, S. (2006). "Subacute Sclerosing Panencephalitis (SSPE) Overview of Clinical Manifestations." Pediatric Neurology, 34(5), 268-270.

2. Rota, P. A., et al. (2016). "Measles." In Plotkin's Vaccines (7th ed., pp. 579-618). Elsevier.

External Links

- Centers for Disease Control and Prevention (CDC): Measles - Information on measles, its complications, and prevention through vaccination.

• 23-273l. at Merck Manual of Diagnosis and Therapy Home Edition

• subacute_panencephalitis at NINDS

• PubMed Health: Subacute sclerosing panencephalitis
• synd/1889 at Who Named It?

Classification	ICD-10: A81.1 ICD-9-CM: 046.2 OMIM: 260470 DiseasesDB: 12597
External resources	MedlinePlus: 001419 Orphanet: 2806

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