Viral infections chronic parenchymal disorders

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PROGRESSIVE RUBELLA PANENCEPHALITIS

Similar to SSPE with a fatal outcome, caused by rubella virus.

Presents at a later age (10-15 years) Progressive dementia. Ataxia. Spasticity. Myoclonus.

Treatment: No effective treatment

CSF shows high y globulin. EEG does not show periodic complexes of SSPE. Antibodies elevated in serum and CSF to rubella. Biopsy does not show inclusion bodies.

POSTVIRAL OR ACUTE DISSEMINATED ENCEPHALOMYELITIS (see page 510) PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY (see page 511)

PRION DISEASES

Fatal conditions characterised by the accumulation of a modified cell membrane protein - Prion protein or PrP (proteinaceous infectious particle) within the central nervous system.

Clinical features are dependent on site and rate of deposition of PrP. A similar disorder in cattle, bovine spongiform encephalopathy (BSE) may be a source of infection in man.

The Prion theory

Experimental and epidemiological evidence supports transmissibility. Physical properties of the infective agent -heat and radiation resistance and absence of nucleic acid - suggests it is comprised solely of protein. This infectious protein when innoculated modifies normal cell membrane protein which acts as a template for further conversion to abnormal protein. This host-encoded protein accumulates without any inflammatory or immune response. In familial cases a point mutation in the prion gene explains disease susceptibility.

Creutzfeldt-Jacob disease (CJD)

A worldwide disorder with incidence 1:1000000. Familial cases account for 10-15%. Age of onset 50-60 years. Non specific symptoms at onset (anxiety and depression) are rapidly followed by myoclonus, ataxia, akinetic rigid state, dementia. Death within 12 months is usual. A new variant (possibly linked to BSE) has been described in younger patients with a slower time course. Iatrogenic disease occurs following corneal or dural grafts, depth electrodes and cadaveric derived human growth hormone treatment.

Investigation

CSF - usually normal.

EEG - bilateral high voltage sharp waves on a background of slow wave activity. The clinical picture and electroencephalogram suggest the diagnosis only ultimately confirmed at postmortem. — -

Pathology

No abnormality is seen on gross examination Microscopically - Neuronal degeneration occurs with marked astrocytic proliferation and amyloid plaque formation. Vacuolation of glial cells results in a characteristic spongiform appearance. Presymptomatic testing in subjects with family history is available.

Treatment - none available

Vacuolation

Gerstmann Straussler syndrome (GSS)

A similar disorder condition to CJD. Cases are familial and characterised by specific pathology of spongiform changes associated with amyloid plaques containing PrP immunoreactive proteins. Clinical features are nonspecific - ataxia, Parkinsonism, dementia. Death occurs within 5 years of contact.

Kuru

An extensively studied disorder of Papua, New Guinea. It is of interest in view of man to man spread from cannibalism.

Prions may have a role to play in other neurodegenerative disorders, e.g. Alzheimer's disease, Parkinson's disease 490 and motor neurone disease.

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