Cerebral MRS in infant with suspected Reye's syndrome

Proton nuclear magnetic resonance-based metabonomics for rapid diagnosis of meningitis and ventriculitis

BACKGROUND

Reduction of mortality associated with bacterial meningitis and postsurgical cerebral ventriculitis is dependent on early diagnosis and institution of appropriate therapy. Metabonomics rapidly defines metabolic profiles of biological fluids through the use of high-throughput analytical techniques combined with statistical pattern recognition tools.

METHODS

Proton nuclear magnetic resonance (1H NMR)-based metabonomics was applied to (1) lumbar cerebrospinal fluid samples collected prospectively from a cohort of patients with bacterial, fungal, or viral meningitis and from control subjects without neurological disease and (2) ventricular cerebrospinal fluid samples from patients with ventriculitis associated with an external ventricular drain and from control subjects. 1H NMR spectra were analyzed by the unsupervised statistical method of principal components analysis.

RESULTS

Metabonomic analysis clearly distinguished patients with bacterial or fungal meningitis (11 patients) from patients with viral meningitis (12) and control subjects (27) and clearly distinguished patients with postsurgical ventriculitis (5) from postsurgical control subjects (10). Metabolites of microbial and host origin that were responsible for class separation were determined. Metabonomic data also correlated with the onset and course of infection in a patient with 2 episodes of bacterial ventriculitis and with response to therapy in another patient with cryptococcal meningitis.

CONCLUSIONS

Metabonomic analysis is rapid, requires minimal sample processing, and is not targeted to specific microbial pathogens, making the platform potentially suitable for use in the diagnostic laboratory. This pilot study indicates that metabonomic analysis of cerebrospinal fluid is feasible and a potentially more powerful diagnostic tool than conventional rapid laboratory indicators for distinguishing bacterial from viral meningitis and for monitoring therapy. This should have important implications for early management, reduced empirical use of antibiotics, and treatment duration.

Brain glutamine by MRS in a patient with urea cycle disorder and coma

In patients who undergo metabolic decompensation from urea cycle disorders, cerebrospinal fluid glutamine level may be a better marker of cerebral dysfunction than blood ammonia or glutamine levels. However, obtaining cerebrospinal fluid by lumbar puncture carries risk in these acutely ill patients with cerebral edema. Using magnetic resonance single voxel spectroscopy as an alternative to cerebrospinal fluid analysis, elevated brain glutamine/glutamate complex levels were detected in a patient with carbamyl phosphate synthetase deficiency, who had been comatose for many days after normalization of blood ammonia and improvement in blood glutamine levels. Brain glutamine by single voxel spectroscopy decreased toward normal with neurologic recovery. We conclude that brain glutamine may be a better marker than serum ammonia for the management of urea cycle disorders, particularly in patients with prolonged mental status changes.

Efficacy of proton magnetic resonance spectroscopy in clinical decision making for patients with suspected malignant brain tumors

We wished to determine the utility of single voxel proton (1H) magnetic resonance spectroscopy (MRS) when used as an alternative or adjunct to brain biopsy in patients harboring lesions suggestive of brain tumors identified by MRI scan. Fifteen patients (age 7-58 years) with MRI scans and clinical histories suggestive of primary brain tumors underwent single voxel 1H-MRS. MRS (16 regions of interest in 15 patients) was used to aid in differentiation between tumor and other pathologies such as stroke or demyelinating plaque (n = 6), radiation necrosis (n = 5), or edema (n = 5). Spectra were quantified to determine absolute molar values of N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), lactate (LAC), and myo-inositol (mI), metabolite ratios relative to Cr were calculated, and spectra were interpreted based on metabolite ratios. Subsequent clinical management was based on MRS interpretation, and patients were then followed to determine if MRS interpretation accurately predicted clinical outcome or surgical findings. Mean follow-up was 12.5 months (range 3-28 months). MRS suggested the presence of recurrent tumor in 7 cases, all of which were subsequently 'confirmed' by tumor resection (n = 4) or disease progression (n = 3). MRS suggested the presence of new tumor in 1 case, subsequently confirmed by surgical resection. MRS suggested the presence of necrosis in 3 patients; all 3 remained radiographically stable during the follow-up period, and one was confirmed by stereotactic biopsy. MRS suggested non-neoplastic lesions in 4 cases, 3 of whom were followed until radiographic resolution of lesions and one of which was confirmed as a pyogenic abscess via stereotactic aspiration. Overall, MRS accurately predicted the pathological nature and clinical outcome of lesions in 15/16 (96%) situations, influenced clinical decision making in 12 cases, and altered surgery planning in 7 patients. In appropriate circumstances MRS can reduce the need for biopsy, and provide an important guide for clinical decision-making in difficult cases.

In vivo proton magnetic resonance spectroscopy in a case of Reye's syndrome

A case of a 14-year-old boy with Reye's syndrome (RS) and complete neurologic recovery is presented. 1H magnetic resonance spectroscopy was performed on days 1 (admission to ICU), 8 and 62: During the acute phase of RS substantial cerebral metabolic imbalances were observed and their normalization monitored. The spectra from day 1 featured extremely high glutamine content (approximately 18 mmol/kg excess) and low concentrations of choline compounds pounds (approximately 1 mmol/kg deficit). Also some excess lactate was present. The subsequent spectra demonstrated the return to an almost normal brain metabolite profile.

15N n.m.r. measurement of the in vivo rate of glutamine synthesis and utilization at steady state in the brain of the hyperammonaemic rat

The rate of glutamine synthesis and utilization at steady state was measured in vivo in the brains of hyperammonaemic rats by 15N n.m.r. in combination with biochemical techniques. Rats were given an intravenous 15NH4+ infusion at the rate of 4.8 +/- 0.3 mmol/h per kg body wt. for 3.5 +/- 0.2 h, followed by 14NH4+ infusion at the same rate for an additional 5.1 h (chase period). During the chase period, blood ammonia (0.61 +/- 0.015 mumol/g), brain ammonia (2.9 +/- 0.3 mumol/g), glutamate (9.4 +/- 0.8 mumol/g) and glutamine (15N + 14N; 14.4 +/- 1.3 mumol/g) were at steady state. The rate of change in the cerebral [5-15N]glutamine concentration was measured in vivo by 15N n.m.r. at 20.27 MHz. To estimate 15N enrichment of precursor ammonia for glutamine synthetase (GS) in astrocytes which are interposed between cerebral capillaries and neurons, 15N enrichments of blood and brain ammonia were measured by gas chromatography-mass spectrometry. The in vivo rate of glutamine synthesis, which is equal to the rate of glutamine utilization at steady state, was estimated, from the observed rate of change in [5-15N]glutamine concentration and 15N enrichment of brain glutamine, to be 4.8 +/- 1.1 mumol/h per g of brain if 15N enrichment of ammonia at the site of GS in astrocytes is equal to that of blood-borne ammonia, and 13.0 +/- 3.9 mumol/h per g if it is equal to that measured for the whole brain. The observed GS activity in vivo in the brain of the hyperammonaemic rat is 2-5% of the reported optimum activity in vitro measured at enzyme-saturating concentrations of all substrates. The result suggests that substrates and/or cofactors other than ammonia kinetically limit GS activity in vivo. The g.c. chromatogram and mass spectrum of ammonia-derived N-trifluoroacetyl-dibutylglutamate (TAB-glutamate) are shown in Supplementary Publication SUP 50170 (4 pages), which has been deposited at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire, U.K., from whom copies can be obtained on the terms indicated in Biochem. J.