Post-traumatic dystrophy (PD) was initially known as Sudeck's atrophy (extensively written about by German surgeon Paul Sudeck (1866-1945)) and has now officially been defined as Complex Regional Pain Syndrome (CRPS). The chronic systemic disease remains a poorly understood condition that can cause severe pain to a limb (often hand or foot) after a trauma. This was often a remarkably small or relatively trivial injury such as a slight sprain or prick of a needle or thorn. CRPS is associated with the deregulation of the autonomic nervous system, causing an error during recalibration that results in persistent pain. The condition has also been noted to occur spontaneously.