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A Study of N-Acetyl aspartic acid/Creatine Ratio in the White Matter of HIV Positive Patients and Its Application

A total of 50 patients were enrolled in the study, and MRI brain with MR spectroscopy was done. Tuberculosis was the most common neurologic disease found in the HIV positive group, consisting of 9 patients. Seven of these patients had tuberculous meningitis amongst which a further 2 had vasculitic infarcts.PML was seen in 6 patients. NAA to Cr ratio was found to be reduced in all the patients, and in fact the value was further reduced compared to the HIV positive group as a whole. Raised choline and myoInositol peaks were also found in all the patients. MR Spectroscopy showed lipid lactate peaks confirming the diagnosis. 2 patients had HIV encephalopathy on the imaging study. Their spectra also revealed lowered NAA peaks along with raised choline peaks. 2 patients with cryptococcosis showed characteristic imaging finding of enlarged Virchow Robin (perivascular) spaces. They revealed elevated choline peaks in addition to reduced NAA. The values of NAA to Cr ratio were determined after duly processing the spectroscopic data from both cases and controls. Each group (Cases and controls) were divided on the basis of age into two age groups: Lesser than or equal to 40 years, and greater than 40 years. In all three groups the values of the mean NAA to Cr ratio ratio was significantly (p-value less than 0.05) reduced in comparison to controls. An ancillary finding was the reduction of NAA to Cr ratio further in cases of PML. Combined use of both the conventional and advanced MRI sequences is advisable as spectroscopy helps in confirming the diagnosis of opportunistic infection of the CNS in HIV positive patients. NAA to Cr ratio ratio is reduced in HIV positive patients and is a marker for HIV infection of the brain even in the absence of imaging findings of HIV encephalopathy or when the patient is symptomatic due to neurological disease of other etiologies.