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. Out of these, 35 were HIV positive patients (cases). 15 patients with HIV negative status who also underwent MRI for unrelated pathologies were enrolled as controls. They also underwent MRI brain with MR spectroscopy. Tuberculosis was the most common neurologic disease found in the HIV positive group, consisting of 9 patients. Two patients had healed granulomas. Seven of these patients had tuberculous meningitis amongst which a further 2 had vasculitic infarcts. Another two in this group had tuberculomas. Prominent lipid lactate peaks on the spectra obtained from the lesions confirmed the diagnosis of tuberculoma. PML was seen in 6 patients. NAA/Cr 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. Toxoplasmosis was seen in 4 patients. MR Spectroscopy showed lipid – lactate peaks confirming the diagnosis. A single patient with brain abscess was seen where also the spectroscopic data from the lesion confirmed the diagnosis with a lactate peak as well as amino acid resonances at characteristic locations. 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. No trehalose peaks were identified. MR Spectroscopy was also done in 4 patients of vascular thrombosis, two arterial and two venous, where the MR Spectroscopic findings were not specific. In 7 patients no focal lesions could be identified on conventional MRI sequences however on MR spectroscopic analysis NAA was found to be reduced in comparison to the controls. The values of NAA/Cr 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/Cr ratio was significantly (p-value less than 0.05) reduced in comparison to controls. An ancillary finding was the reduction of NAA/Cr further in cases of PML. Combined use of both the conventional and advanced MRI sequences is advisable …