Encephalitis lethargica, an epidemic neurological illness, typically involved a severe sleep disorder and progressive parkinsonism. A century later, our understanding relies on seminal descriptions, more recent historical research and the study of small numbers of possible sporadic cases. Theories around infection, environmental toxins, catatonia and autoimmune encephalitis have been proposed. We aimed to describe the presentation of encephalitis lethargica and test these diagnostic and aetiological theories. Subjects with encephalitis lethargica were identified in the archives of the National Hospital for Neurology and Neurosurgery, UK between 1918 and 1946. Case notes were examined to establish illness temporality, clinical features and cerebrospinal fluid results. Controls from the archives were identified for 10% of cases, matching on discharge year, sex and neurologist. Clinical presentation was compared to modern diagnostic criteria for encephalitis lethargica, catatonia and autoimmune encephalitis. In a case-control design, a multilevel logistic regression was conducted to ascertain whether cases of encephalitis lethargica were associated with febrile illnesses and with environmental exposures. Six hundred and fourteen cases of encephalitis lethargica and 65 controls were identified. Cases had a median age of 29 years (interquartile range 18) and a median time since symptomatic onset of 3.00 years (interquartile range 3.52). Motor features were present in 97.6%, cranial nerve findings in 91.0%, ophthalmological features in 77.4%, sleep disorders in 66.1%, gastrointestinal or nutritional features in 62.1%, speech disorders in 60.8% and psychiatric features in 53.9%. Of the 167 cases who underwent lumbar puncture, 20 (12.0%) had a pleocytosis. The Howard and Lees criteria for encephalitis lethargica had a sensitivity of 28.5% and specificity of 96.9%. Among the cases, 195 (31.8%, 95% confidence interval 28.1-35.6%) had a history of febrile illness within one calendar year prior to illness onset, which was more common than among the controls (odds ratio 2.70, 95% confidence interval 1.02-7.20, P = 0.05), but there was substantial reporting bias. There was no evidence that occupational exposure to solvents or heavy metals was associated with encephalitis lethargica. Two hundred and seventy-six (45.0%) of the cases might meet criteria for possible autoimmune encephalitis, but only 3 (0.5%) might meet criteria for probable NMDA receptor encephalitis. Only 11 cases (1.8%) met criteria for catatonia. Encephalitis lethargica has a distinct identity as a neuropsychiatric condition with a wide range of clinical features. Evidence for a relationship with infectious or occupational exposures was weak. Autoimmune encephalitis may be an explanation, but typical cases were inconsistent with NMDA receptor encephalitis.

The hormone prolactin (PRL) is best recognised for its indispensable role in mammalian biology, specifically the regulation of lactation. Bearing in mind that the mammary gland is a modified sweat gland, it is perhaps unsurprising to discover that PRL also plays a significant role in cutaneous biology and is implicated in the pathogenesis of a range of skin diseases, often those reportedly triggered and/or exacerbated by psychological stress. Given that PRL has been implicated in over 300 biological processes, spanning reproduction and hair growth and thermo- to immunoregulation, a comprehensive understanding of the relationship between PRL and the skin remains frustratingly elusive. In an historical curiosity, the first hint that PRL could affect skin biology came from the observation of seborrhoea in patients with post-encephalitic Parkinsonism as a result of another global pandemic, encephalitis lethargica, at the beginning of the last century. As PRL is now being postulated as a potential immunomodulator for COVID-19 infection, it is perhaps timeous to re-examine this pluripotent hormone with cytokine-like properties in the cutaneous context, drawing together our understanding of the role of PRL in skin disease to illustrate how targeting PRL-mediated signalling may represent a novel strategy to treat a range of skin diseases and hair disorders.

One hundred years ago, an influenza pandemic swept across the globe that coincided with the development of a neurological condition, named "encephalitis lethargica" for the occurrence of its main symptom, the sudden onset of sleepiness that either developed into coma or gradually receded. Between 1917 and 1920, mortality of the flu was >20 million and of encephalitis lethargica approximately 1 million. For lessons to be learned from this pandemic, it makes sense to compare it with the COVID-19 pandemic, which occurred 100 years later. Biomedical progress had enabled testing, vaccinations, and drug therapies accompanied by public health measures such as social distancing, contact tracing, wearing face masks, and frequent hand washing. From todays' perspective, these public health measures are time honored but not sufficiently proven effective, especially when applied in the context of a vaccination strategy. Also, the protective effects of lockdowns of schools, universities, and other institutions and the restrictions on travel and personal visits to hospitals or old-age homes are not precisely known. Preparedness is still a demand for a future pandemic. Clinical trials should determine the comparative effectiveness of such public health measures, especially for their use as a combination strategy with vaccination and individual testing of asymptomatic individuals. It is important for neurologists to realize that during a pandemic the treatment possibilities for acute stroke and other neurological emergencies are reduced, which has previously led to an increase of mortality and suffering. To increase preparedness for a future pandemic, neurologists play an important role, as the case load of acute and chronic neurological patients will be higher as well as the needs for rehabilitation. Finally, new chronic forms of postviral disease will likely be added, as was the case for postencephalitic parkinsonism a century ago and now has occurred as long COVID.

We describe the Italian contribution to the description and treatment of parkinsonism following encephalitis lethargica (EL): postencephalitic parkinsonism (PEP). Special attention is devoted to the description of postencephalitic symptoms by Giuseppe Panegrossi (1871-1953) and to the treatment based on Atropa belladonna introduced in Italy and extensively supported by Arturo Nannizzi (1887-1961), who was charged by the queen of Italy with conducting research into this plant and advocating its cultivation for healing purposes. This article gives us the unique opportunity to revisit the figure of this distinguished botanist, providing a summary of his biography, interests, and achievements.

More than 100 years after its emergence, the exact pathophysiological mechanisms underlying encephalitis lethargica (EL) are still elusive and awaiting convincing and complete elucidation. This article summarizes arguments proposed over time to support or refute the hypothesis of EL as an autoimmune neuropsychiatric disorder triggered by an infectious process. It also provides a critical evaluation of modern cases labeled as EL and a comprehensive differential diagnosis of autoimmune neurological conditions that could mimic EL. The evidence supporting the autoimmune nature of historical EL is sparse and not entirely convincing. It is possible that autoimmune mechanisms were involved in the pathogenesis of this disease as an idiosyncratic response to a yet unidentified infectious agent in genetically predisposed individuals. Although there has been an increase in the incidence of presumed autoimmune encephalomyelitis since the peak of EL pandemics, most evidence does not support an underlying autoimmune mechanism. There are significant differences between historical and recent EL cases in terms of clinical symptomatology, epidemiology, and neuropathological features, suggesting that they are different entities with only superficial similarity. The term "encephalitis lethargica," still frequently used in the medical literature, should not be used for cases occurring at present in the sporadic form. Historical EL should be kept apart from recent EL, as they differ in important aspects. Constantin Alexander von Economo, a psychiatrist and neurologist, reported in 1917 about encephalitis lethargica in front of the Vienna Psychiatric Society. Sporadic cases of this brain and brainstem encephalitis were reported in 1916 and 1917, and similar cases were reported around the world between 1919 and 1920. His primary description of the illness that raged in an epidemic in Europe and North America between 1916 and 1927 was named von Economo encephalitis.  A few weeks before, Jean-Rene Cruchet presented his observations to the Paris Medical Society after treating military patients with neuropsychiatric disorders showing unusual neurological signs. Encephalitis lethargica or von Economo encephalitis is also known as sleeping sickness. Originally it was classified into three clinical forms: somnolent-ophthalmoplegic, hyperkinetic, and amyostatic-akinetic. Currently, postencephalitic parkinsonism has a very close relationship with encephalitis lethargica, also called von Economo encephalitis.  Von Economo was nominated for the 1926, 1930, and 1932 Nobel Prize in Physiology or Medicine. Encephalitis lethargica came to light after the book “Awakening” written by an English neurologist, Oliver Sacks. A movie based on the book was released in 1990.