Encephalitis lethargica

Encephalitis lethargica (EL) is a rare disease that is also, also known as von Economo encephalitis. It, is a rare disease of unknown aetiology that affects the midbrain and basal ganglia, and the exact aetiology is unknown. 

Clinical presentation

Symptoms are initially that of pharyngitis followed by lethargy, extrapyramidal movements (parkinsonism and dyskinesias), neuropsychiatricdisturbance (obsessive, compulsive disorder, catatonia, mutism, apathy and conduct disorders), and ocular movement disorder (oculogyric crises).

Pathology

The exact aetiology is unknown, but there is lymphocyte infiltration of the midbrain and basal ganglia. It is thought that there may be an autoimmune component, possibly triggered after a viral infection.

Markers

Autoantibodies reactive against human basal ganglia antigens present in the majority of ELencephalitis lethargica patients. 

Radiographic features

MRI

Brain MRI demonstrates inflammatory changes localised to the deep grey matterin 40% of patients.

• T1: low signal
• T2/FLAIR: high signal in the basal ganglia (including the substantia nigra), midbrain, thalamus, cerebral peduncle and/or temporal cortex
• T1 C+ (Gd): leptomeningeal and focal patchy enhancement 
• DWI/ADC: isointense without restriction of ADC

Nuclear medicine

• PET-CT:increased glucose metabolism in the basal ganglia

Treatment and prognosis

Treatment approaches to encephalitis lethargica include immunomodulating therapies and steroids.

History and etymology

First described by Constantin Freiherr von Economo in (1876-1931), a Romanian psychiatrist and neurologist, in 1916 during an epidemic affecting 500,000 people worldwide in 1916-1927⁴. There have been no further epidemics of ELencephalitis lethargica since the 1920s, although sporadic cases have continued to be reported.

Differential diagnosis

General imaging differential considerations include:

• limbic encephalitis
• herpes simplex encephalitis
• leptospirosis