Hypercapnia is a possible determinant of the function of the blood-cerebrospinal fluid barrier in amyotrophic lateral sclerosis.

Elevated cerebrospinal fluid (CSF)/serum quotients of albumin (Q(Alb)) may occur in motor neuron diseases (MND) including amyotrophic lateral sclerosis (ALS), but the pathophysiologic mechanisms underlying these alterations are unclear. Evidence from animal experiments suggests that the arterial carbon dioxide level might affect the Q(Alb), i.e. the function of the blood-CSF barrier (BCB). We therefore compared basic CSF parameters in different forms of MND (ALS, n = 105; lower motor neuron diseases, n = 12; and upper motor neuron diseases, n = 7) and investigated the relationship between elevated Q(Alb) and the arterial partial pressure of carbon dioxide (pCO(2)) in ALS where respiratory insufficiency leads to hypercapnia in the course of the disease. Pathologic elevations of Q(Alb) occurred in 32 of 124 MND patients. In ALS, Q(Alb) significantly correlated with the arterial pCO(2) (r = 0.454; P = 0.001; n = 45). These data indicate that BCB dysfunction is a frequent finding in different forms of MND and may reflect distinct pathophysiological mechanisms. In ALS, an important underlying mechanism might be the influence of the arterial pCO(2) which may alter the CSF flow.