Table 1.

Summary of retrospective cohort studies and case series of patients with encephalitis lethargica and tics

Study	Country	Number	Mean age (range)	Male (%)	Aetiology of encephalitis	Tics	Other neuropsychiatric symptoms	Additional findings	Main limitations
Calne et al. [8]	UK	40	47–73	45	Encephalitis lethargica	3 patients developed tics	Parkinsonism reported as very common; 9 patients with psychiatric disturbances (6 aggressive and uncooperative, 1 obsessional, 1 paranoid, 1 depressed); 4 with choreoathetosis	All patients had a history of illness in the 1917 encephalitis pandemic and had been in a hospital for an average of 29 years	Case histories not documented for individual patients; description of tics lacking detail
Sacks et al. [9]	USA	25	N/A	N/A	Encephalitis lethargica	8 patients developed respiratory and phonic tics (sudden deep breaths, yawns, coughs, giggles, sighing, grunting, moaning)	Severe post-encephalitic syndrome, with the development of respiratory crises and tics after treatment with l-dopa	In some cases (not quantified), the respiratory tics and breathing abnormalities were present before the administration of l-dopa and increased after its use	Lack of detail about the presence of tics before the administration of l-dopa and its effects on individual patients
Dale et al. [10]	UK	20	2–69	55	Basal ganglia encephalitis, reported as encephalitis lethargica	2 patients developed tics: a 10-year-old boy had motor tics; a 17-year-old boy had both motor and phonic tics	Hypersomnolence, bradykinesia, mutism, and depression (10-year-old boy); sleep inversion, bradykinesia, stereotypies, mutism, catatonia, obsessive-compulsive disorder, trichotillomania (17-year-old boy)	N/A	Description of tics lacking detail (including data on tic onset)
Dale et al. [11]	Australia	17	7 (0–15)	53	Basal ganglia encephalitis, reported as encephalitis lethargica	1 patient developed motor tics	Somnolence, lethargy, parkinsonism	Diagnosis based on the presence of somnolence, an akinetic movement disorder, and emotional dysregulation in the background of basal ganglia changes on neuroimaging	Demographic data of individual patients not reported; description of tics lacking detail