Historical study of coma: looking back through medical and neurological texts

In the 1960s, two major works on coma by Fisher, Plum and Poser were published and ushered in the beginning of a comprehensive clinical examination in coma. How these ideas matured has been rarely investigated. In this article, we describe observations and experiments that led to a better understanding of consciousness and coma in medical texts prior to that episode. We consulted medical texts published between 1640 and 1960. Subject indexes and tables of contents of textbooks were reviewed for the words coma, (loss of) consciousness, stupor and somnolence. Chapters on apoplexy were reviewed for descriptions of impaired consciousness. We found information on terminology, classification, causes, observation and examination, pathophysiology, treatment and experimental coma. Up to the middle of the 19th century, disorders of sense, motion and breathing, and also changes in the patient's pulse, were recognized as clinical cues. The distinction between a structural and toxic (endogenous and exogenous) cause was recognized early. Observed phenomena were explained from the perspective of humoral medicine and treated likewise. After the middle of the 19th century, specialization in medicine and experimental research of intracranial pressure resulted in important insights and more accurate clinical examination. Cranial surgery and the discovery of the brainstem reticular activating system in the first half of the 20th century contributed to further increases in knowledge. The understanding, clinical examination and treatment of coma has gone through a gradual evolution over many decades. The recapitulation of clinical signs in impaired consciousness into a teachable and reproducible module marks an abrupt change in clinical approach. This transition is very recent, based on close clinical observation and interpretation of experimental and pathology studies and less on modern neuroimaging.