Subacute Sclerosing Panencephalitis (Dawson Disease)
What is Subacute Sclerosing Panencephalitis?
Subacute sclerosing panencephalitis (SSPE) is a chronic persistent infection of the central nervous system caused by an altered form of the measles virus. It affects primarily children and young adults and usually has a progressive downhill course which results in death within a few years in most patients with a 5% chance of spontaneous remission. It can occur anywhere from 2 to 10 years after the original measles illness, and generally results in progressive neurological deterioration due to brain inflammation and nerve cell death. Since the widespread use of the measles vaccine, SSPE has become very rare. However, studies have shown that the incidence of SSPE has remained high in the Middle East and India. Initial symptoms usually include abnormal behaviour, irritability, intellectual deterioration, and memory loss which may be followed by involuntary movements and seizures (in the form of myoclonic spasms). Subsequently, the patient develops further mental deterioration, inability to walk, speech impairment with poor comprehension, and difficulty swallowing (dysphagia). Blindness may also result. In the final stages of disease, the patient may remain mute or comatose. The electrical activity of the brain, as recorded by electroencephalogram (EEG), shows progressive changes during the disease which are typical of SSEP and parallel the slow deterioration of central nervous system functions. A number of clinical staging scales have been used for several decades to categorize patients with SSPE according to their corresponding clinical status. More recently, a different staging system was developed based on the radiological findings of the brain by computed tomography (CT) and magnetic resonance imaging (MRI). This method, however, has not succeeded in establishing a complete correlation between radiological abnormalities and clinical progress.