Also known as Magnan-Saury's sign and cocaine bugs. The eponym Magnan's sign refers to the French alienist Jacques Joseph-Valentin Magnan (1835-1916), who described the concomitant phenomenon in 1889 in a paper co-authored by a pupil named Saury (hence the second eponym, Magnan-Saury's sign). Both eponyms refer to a crawling, " tactile hallucination of a foreign body under the skin that is associated with the chronic use of cocaine. Save the association with cocaine, Magnan's sign is comparable with "formication.
References
Magnan, V., Saury, M. (1889). Trois cas de cocainisme chronique. Comptes Rendus Hebdomadaires des Séances et Mémoires de la Société de Biologie, 41, 60-63.
Dictionary of Hallucinations. J.D. Blom. 2010.