Value of lumbar puncture in the diagnosis of genetic metabolic encephalopathies

Diagnostic testing for genetically determined metabolic disease has for man y years relied heavily on the use of generalized screening tests that analy ze groups of related compounds in easily accessible peripheral fluids such as plasma and urine. Organic: acid profiles in urine and amino acid analysi s in plasma are two of the most commonly requested tests; these, together w ith other protocols that examine peripheral fluids, have been and continue to be invaluable tools. There is, however an emerging realization that many metabolic encephalopathies do not arise secondary to peripheral metabolic changes but rather have their origins within the central nervous system. In these cases, testing of peripheral fluids might be uninformative. This rev iew is designed to examine the role:of cerebrospinal fluid analyses in the investigation of infants and children with undefined encephalopathies. The aims are to review the conditions in which measurement of metabolites in ce rebrospinal fluid is critical if a diagnosis is to be made, and to emphasiz e that considerable forethought is often required to ensure correct collect ion and handling of cerebrospinal fluid. Thus, fidelity of the diagnostic a nalytic procedures is maintained. This review will help the pediatric neuro logist establish practical diagnostic guidelines that in turn mill help in the recognition of recently described conditions.:Those conditions can, in general, be identified only after specialized cerebrospinal fluid testing.