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Cerebrospinal fluid beta‐2‐microglobulin: A reliable index of leukaemic infiltration of central nervous system

Cerebrospinal fluid (CSF) beta‐2‐microglobulin (B2m) has been proposed as a marker of central nervous system (CNS) involvement in myelo‐lymphoproliferative diseases. Recently its reliability has been put in question because of false positive and false negative results. In our study, B2m was measured in 574 CSF samples collected from 74 patients affected by ALL, ANLL or lymphomas; 20 of these patients had CNS‐involvement while they were under observation. There was a significant difference in CSF B2m between the patients with and without CNS‐involvement (p < 0.001). No false positive or false negative results were obtained. In 4 cases the rising of CSF B2m was observed 8, 6, 4 and 4 wk before the clinical and laboratory diagnosis of CNS‐involvement. In all patients the clinical and laboratory improvement of the neurological disease was associated with a progressive decrease of CSF B2m. Some hypotheses about the origin of CSF B2m are discussed. The authors conclude that CSF B2m is a useful and reliable marker of CNS‐involvement in myelo‐lymphoproliferative disease.