Portosystemic myelopathy: spastic paraparesis after portosystemic shunting

Portosystemic encephalopathy (PSE) is a well-known, common complication of portal hypertension. It is thought to be caused by nitrogenous substances such as ammonia, which are normally cleared from the blood stream by the liver. In cirrhosis and other hepatic disorders with portosystemic shunting (PSS)-- either surgical portosystemic anastomoses (PSA) or spontaneous PSS-- the collateral vessels bypass the liver allowing the accumulation of toxic, ammoniacal substances in the blood and tissues. PSE is characterized by encephalopathy; portosystemic myelopathy (PSM) is characterized by paresis of the extremities, Babinski signs and muscle spasticity in patients with cirrhosis and/or PSS. Usually only the lower extremities are involved. This report presents the first case of this syndrome observed 5 years after a transjugular intrahepatic portosystemic shunt. The 31 year old man with chronic Hepatitis B developed complete spastic paraparesis within 4 weeks after onset of clinical/neurological symptoms, accompanied by an episode of severe hepatic encephalopathy. The transcortical magnetic stimulation showed normal motoric stimulation times to the abductor digiti minimi muscles but no stimulation to the tibialis muscles was seen. Lumbar stimulation to the tibialis muscles, however, was normal. This indicates loss of motor neurons in the spinal cord, a characteristic finding in patients with portosystemic myelopathy. We performed a search of the literature for all reported cases of cirrhosis and/or PSS that developed PSM. However, the intervals between the construction of a shunt and the diagnosis of portosystemic myelopathy were shorter in total portacaval shunts (median 16 months) than in partial, non-portacaval shunts (median 60 months, p < 0.01). This suggests that not only the shunt itself but also the shunted volume contributes to the development of the syndrome Sixty-one patients with PSM have been reported in the literature since 1944. PSE had developed before PSM in almost all cases. PSM occurred from 1 month to 10 years after the creation of portacaval anastomoses (PCA) or splenorenal shunts (SRS) or in cirrhotic patients without shunts. No one type of liver disease or type of shunt appears to predispose to PSM. The mechanisms of PSE and PSM are thought to be similar and of nitrogenous origin, but their pathogenesis remains unknown. Lathyrism, a toxic syndrome with similar symptoms and signs, is caused by the ingestion of a legume, Lathyrus sativa, which contains beta-N-oxalo-L amino-L-alanine (BOAA). This animal model with or without BOAA appears to offer a reliable way of studying PSM experimentally.