First Clinical Description of Polio
In 1789, British physician specializing in midwifery and surgery, Michael Underwood, published A Treatise on the Diseases of Children, with General Directions for the Management of Infants from Birth, which details diseases and their origins that particularly affected children. Of particular note was his description of polio, noting it as "debility of the lower extremities".
References:
Dunn, P M. “Michael Underwood, MD (1737-1820): physician-accoucheur of London.” Archives of disease in childhood. Fetal and Neonatal Edition vol. 91,2 (2006): F150-2. doi:10.1136/adc.2005.074526
"Michael Underwood (1736?-1820)." Vaulted Treasures: University of Virginia, Historical Collections at the Claude Moore Health Sciences Library, http://exhibits.hsl.virginia.edu/treasures/michael-underwood-1736-1820/.