(NIGH-trik OK-side) A molecule that helps muscles stay smooth and relaxed. A shortage of nitric oxide can occur in paroxysmal nocturnal hemoglobinuria paroxysmal nocturnal hemoglobinuria: (par-uk-SIZ-muhl nok-TURN-uhl hee-muh-gloe-buh-NYOOR-ee-uh) A rare and serious blood disease that causes red blood cells to break apart. Paroxysmal means sudden and irregular. Nocturnal means at night. Hemoglobinuria means hemoglobin in the urine. Hemoglobin is the red part of red blood cells. A… (PNH), causing muscle spasms in certain parts of the body.
