Platypnoea-orthodeoxia: a rare cause of severe dyspnoea.

Platypnoea-orthodeoxia is a relatively unknown syndrome characterized by dyspnoea and arterial desaturation during the transition from a lying to an uprighth position by right to left shunting of blood without increased blood pressure in the right atrium. The condition is assumed to be underdiagnosed because of challenging diagnostics. This case describes a woman who, despite extensive investigation, remained undiagnosed for years. The diagnosis should be kept in mind when treating unexplained desaturation.