Cerebrospinal-fluid lactate in adult mitochondriopathy with and without encephalopathy.

Despite improved diagnostic facilities, the diagnosis of mitochondriopathy (MCP) is sometimes difficult to establish. This study aimed to investigate whether CSF lactate can be of diagnostic help in this respect. Cerebrospinal-fluid (CSF) lactate and its relation to resting lactate and lactate stress testing were investigated in 26 MCP patients, aged 30-84 years. The upper reference limit of CSF lactate, obtained from 28 healthy subjects, was 1.6 mmol/l. Seven MCP patients (27%) had elevated CSF lactate. Five of these patients had central nervous system (CNS) abnormalities other than elevated CSF lactate. In two patients with increased cerebrospinal-fluid lactate, lactate stress testing was normal or could not be carried out. In conclusion, CSF lactate is elevated in one quarter of adult MCP patients. CSF lactate is preferentially elevated in patients with additional CNS abnormalities other than elevated CSF lactate. If the results for resting lactate or lactate stress testing are normal or unavailable, determination of CSF lactate may be of diagnostic support in single cases.