Westphal is credited with describing a deep tendon reflex anomaly in tabes dorsalis that later became known as the "Erb–Westphal symptom" (named with neurologist Wilhelm Heinrich Erb (1840–1921). His name is also shared with neurologist Ludwig Edinger (1855–1918) regarding the Edinger–Westphal nucleus, which is an accessory nucleus of the oculomotor nerve (cranial nerve number III; CN III). He was the first physician to provide a clinical description of narcolepsy and cataplexy (1877). French physician Jean-Baptiste-Édouard Gélineau (1828–1906), also described the two maladies, coining the term "narcolepsie" in 1880.