PET and SPECT Scans Not the Same
These researchers did note, however, that the findings from FDG-PET scans did not correlate with those from SPECT scans of the patients, where available. Nine patients had previous SPECT scans, one of which was normal, with the remainder showing evidence of diffuse cortical hypoperfusion (poor blood flow in a number of areas of the brain). The PET scans for these eight patients differed substantially with three showing no abnormalities, three showing bitemporal hypometabolism, one with hypometabolism in the basal ganglia alone, and one with globalhypometabolism. The discrepancy between the scans was not explained by Hurley and Taber but suggests that cererbral metabolism (as shown on PET scans) and cerebral blood flow (as shown on SPECT scans) are not necessarily affected in a similar fashion in Lyme disease patients. An FDG-PET is a non-invasive diagnostic tool that may be used to diagnose cancer as it can yield information on blood flow, the health of cells, and the metabolic activity of tissues. The substances used in such tests (such as sugars, amino acids, hormones, and metabolic precursors) are labelled with positron-emitting radioisotopes that are then detectable on PET scans.
SPECT Scans and MRIs for Lyme Disease
Differences in demonstrating abnormalities in the brain also exist between SPECT scans and MRI scans for Lyme disease. The same study as above (Hurley and Taber, 2008) found that in the group of patients with confirmed Lyme encephalopathy, almost all (11/13) had a normal MRI scan, with just two showing areas of enhancement of white matter suggestive of lesions. In contrast, all of the patients (13/13) had abnormalities on SPECT scans where multiple areas of hypoperfusion were evident involving both cortical and subcortical involvement. The most common areas affected by poor blood flow were the lateral and medial frontal cortices, medial temporal cortices, fronto-temporal white matter, and basal ganglia. Following a four-week course of Lyme disease antibiotic treatment most patients in the Lyme encephalopathy group showed clear improvements in neuropsychiatric symptoms with improvements observed between one and three months after the treatment. Follow-up SPECT scans taken at six months after treatment showed improvements in brain blood flow in all of the patients.
Evidence for the Use of SPECT Scans for Lyme Patients
Other evidence of the possible usefulness of SPECT scans in Lyme disease diagnosis and treatment comes from Donta (2003), although the stringency of his criteria for inclusion in this paper has been questioned by other doctors working in the field of Lyme disease research. Donta looked at 183 patients who fit the ‘clinical definition of chronic Lyme disease’, which is itself difficult to comprehend, given the lack of recognition of ‘chronic Lyme disease’ in official Lyme disease guidelines as given by the CDC and IDSA. Nonetheless, the patients determined to be suffering from chronic Lyme disease and who were suffering from cognitive and/or mood dysfunction were found to display abnormalities on SPECT scans in 75% of cases. Abnormal blood flow (perfusion) in the temporal lobes was noted in 46% of patients, 40% showed frontal lobe perfusion abnormalities, and 33% had altered blood flow in the parietal areas. Of those patients with perfusion abnormalities, 53% were considered to be mild differences, 32% moderate, and 15% severe. Patients who had suffered symptoms for more than a year were more likely to have perfusion defects (80% compared to 50%).
SPECT Scans Reveal Abnormal Brain Blood-Flow in Lyme Patients
Donta observed that those patients treated with either tetracycline or a combination of clarithromycin and hydroxychloroquine showed improvements in the abnormal brain blood-flow in 70% of cases over a one-year period. The problems with such research include the lack of a control group, the poor specificity of criteria for inclusion in the patient group and the relative subjectivity of those criteria in terms of symptoms. Without knowing the rate of mild perfusion abnormalities in other people, not suffering from Lyme disease but with similarly affected cognition or mood it is difficult to establish the association between the results of SPECT scans and Lyme disease pathology. A previous criticism of the work done by Donta noted that applying his diagnostic criteria to the general population would result in 40% of people being diagnosed with Lyme disease (Wormser, et al, 2007). Clearly more high quality, double-blind, placebo-controlled research needs carrying out into the potential benefits of using Lyme disease SPECT scans before such methods become part of standard Lyme disease management.
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Wormser, G.P., Dattwyler, R.J., Shapiro, E.D., Steer, A.C., Klempner, M.S., Krause, P.J., Bakken, J.S., Strle, F., Stanek, G., Bockenstedt, L.K., Fish, D., Dumler, J.S., Nadelman, R.B., Reply to Pollock, Donta, Wilson, and Arne, Clin Infect Dis. (2007) 44 (8):1137-1139.
Donta, S.T., Interscience Conference on Antimicrobial Agents and Chemotherapy (43rd: 2003: Chicago, Ill.). Abstr Intersci Conf Antimicrob Agents Chemother, 2003 Sep 14-17; 43: abstract no. L-186.
Hurley, R.A., Taber, K.H., Acute and Chronic Lyme Disease: Controversies for Neuropsychiatry, J Neuropsychiatry Clin Neurosci 20:iv-6, February 2008.