Ernest-Charles Lasègue was a remarkable figure in the history of 19th-century French medicine (Fig. 1). Along with Jean-Martin Charcot (French neurologist contemporary of Lasègue), he made great inroads into the fields of neurology and psychiatry [2, 3].

Fig. 1
figure 1

Ernest-Charles Lasègue (1816–1883)

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Lasègue was born on September 5, 1816, in Paris. His father, Antoine Lasègue, was a botanist and worked as a librarian [7]. The intelligent young Lasègue began his scientific education in his native city at Lycée Louis-le-Grand. In his youth, he studied philosophy and rhetoric, could speak Latin fluently, and could translate a Greek text on philosophy after his first reading of it. In 1838, at the age of 22, Lasègue became a teacher at the aforementioned school [2, 3, 7]. At this time, Lasègue’s friendship with Claude Bernard (French physiologist) became a turning point in his career. Their friendship convinced him to study medicine. In 1839, Lasègue attended the lectures of Armand Trousseau (French internist) and first expressed his interest in studying medicine. He registered at the Faculté de Médecine (Faculty of Medicine) and enthusiastically began his education. Later, he became Trousseau’s assistant, collaborator, and favorite pupil [2, 7].

In 1846, Lasègue earned his medical doctorate from the University of Paris with a thesis entitled De Stahl, et de sa Doctrine Médicale (Stahl and His Medical Doctrine) [2, 3, 7]. He then became a consulting physician at the Préfecture de Police (Police Prefecture) in Paris. This career provided him the opportunity to examine a large number of people accused of different crimes. Lasègue wrote standardized notes on this group of patients and their manifestations and later published an article on his findings [5, 7, 10].

From 1852 to 1854, Lasègue served as Trousseau’s Chef de Clinique (Head of Clinic). In 1853, he earned the title of Professeur Agrégé (Associate Professor) with a thesis on paralytic dementia entitled De la Paralysie Générale Progressive (Progressive General Paralysis) [2, 5, 7]. In that same year, he joined Francois Folline and Francois Valleix as co-editors of the Archives Générales de Médecine (Archives of General Medicine), the journal in which he published most of his articles [2, 5]. Lasègue also became a physician at the Salpêtrière, Pitié, and Necker Hospitals [2]. In 1862, he was appointed Lecturer on Mental and Nervous Diseases; in 1867, he was appointed Professor of General Pathology [2, 3, 7]. In 1869, he became the Chair of Clinical Medicine at La Pitié Hospital, a position he held until his death in 1883 from complications of diabetes at the age of 67 [7].

Lasègue published about 115 scientific papers on different medical topics in the areas of neurology, psychiatry, internal medicine, pediatrics, and the history of medicine. It is worth noting that Lasègue’s knowledge of languages other than his native tongue allowed him to familiarize himself with English and German scientific literature [7].

Lasègue is mainly recalled by the eponym Lasègue’s sign (also known as Lasègue’s test or straight leg raising test), a clinical finding that is helpful in the diagnosis of sciatica. This clinical manifestation is characterized by painful flexion of the hip when the knee is extended (pain that is not present at the time of knee flexion). This sign is considered to be his main contribution to the field of neurology [2, 9]. It is interesting to note that Lasègue himself did not write about this manifestation [7]. In 1881, some years after his death, his pupil, J.J. Forst, introduced this clinical finding in his thesis entitled Contribution à L’étude Clinique de la Sciatique (Contribution to the Clinical Study of Sciatica) and attributed it to his teacher [1, 4, 9].

Lasègue was a pioneer of objective psychology on the basis of meticulous clinical observations. It was his belief that recording a detailed history of the patient was essential to recognizing the cause of mental illness. He emphasized the complementary roles of physiology and psychiatry [2, 3].

Psychosomatic disorders were a main focus of interest for Lasègue [2]. In 1873, in a paper entitled De l’Anorexie Hystérique (On Hysterical Anorexia), he described anorexie hystérique (hysterical anorexia or anorexia nervosa) [3, 6, 8]. Although Lasègue described this disorder about 5 years after the description by William Withey Gull (British physician) of an anorexia-like condition, in fact, it was Lasègue who focused in detail on the psychological symptoms and stressed the role of parental attitudes and family interaction in this disorder [3, 10].

In 1877, together with Jean-Pierre Falret (French psychiatrist), he introduced and explained the concept of folie à deux. Today, this disorder bears the names of both scientists as Lasègue–Falret syndrome [2, 3]. For the first time in medical history, in 1887, Lasègue introduced and described exhibitionism [6]. He also conducted basic studies on persecutory delusion and described this disorder in 1852 [1, 3]. Lasègue is also remembered for Lasègue’s gangrene (a type of gangrene in the bronchus), Lasègue’s disease (paranoia), Lasègue’s syndrome I (persecution mania), and Lasègue’s syndrome II (a disturbance in conversion hysteria) [2].