Introduction: The persistent vegetative state is a clinical defined diagnosis. It is characterized by complete unawareness of the self and the environment, accompanied by sleep wake cycles. Patients show no evidence of behavioural responses to different external stimuli(1). There are a lot of diagnostic, prognostic and therapeutic uncertainties concerning this condition. Sometimes it is difficult to differentiate the PVS from locked-in syndrom or akinetic mutism. There is a lack of tests for objectivation of amount or recovery of cortical functions. Results of electrophysiological methods and imaging are not shure enough for prognostic evalutation.
The 1H magnetic resonance spectroscopy is able to detect non-invasive N-acetylaspartate (NAA), phosphocholine (Ch), phospho-creatine (Cr), lactat and other metabolites. NAA is a marker of neuronal integrity(2). Probably it plays a role in synthesis of lipids and proteins and in metabolism of different neurotransmitters. The loss of NAA seems to be irreversible. In a diagnostic programme we analysed the importance of 1H MRS for the determination of PVS.
The data of spectroscopic examination of 10 patients (group PVS, mean age 44 years) suffered from PVS (hypoxic n=7, posttraumatic n=1, hypoglycaemic n=1, postoperative n=1) were compared to the results of healthy volunteer groups (group I, mean age 26 years; group II, mean age 62 years).
1H MRS was performed with water suppression by selective inversion pules using 1.5 T (Gyroscan S15, Philips). Basing on a transversal T2-weighted imaging (TE = 30; 90 msec / TR = 2000 msec), the volume of interest (20x20x40 mm) was localized by a SPARS-sequence in an occipito-parietal region. The spectra were obtained using a head coil after shimming to minimize magnetic field inhomogenities. We choised the following parameters: TR= 2 sec., TE=136 msec., sample frequency 1 KHz, 1024 samples 256 measurements. In the standard processing of spectra zero filling 4K, fourier transformation and phase correction were used. Evaluation of ratio NAA/Ch by integral of the peaks allowed to discribe metabolic changes mathematically.
In 5 patients there was the acquired spectrum characterized by the complete lack of NAA. The other patients showed different but compared with the volunteers strongly decreased ratio for NAA/Ch.
The reduction of the cerebral metabolic rate in PVS examined by PET is wellknown but does not allow prognostic decisions(3,4). The examination of the cellular metabolism of the brain by 1H MRS is an interesting non-invasive diagnostic possibility in patients with PVS or other severe cerebral disturbances. The lack of NAA can be a sign of complete neuronal damage. It is assumed to be irreversible and could have importance for possibilities of rehabilitation. The correlation with clinical and electrophysiological data such as EEG, SEP, AEP and MEP suggest that 1H MRS can be helpful in confirmation of diagnosis and can provide prognostic evaluation.