Additional investigations
Non-invasive cardiovascular function tests such as standing blood pressure and heart rate, Valsalva maneuver or heart rate variability should be performed to define the pattern and severity of autonomic dysfunction in MSA. However, these tests may be less helpful for differential diagnosis. Non-specific changes in the EEG are also unhelpful for diagnostic purposes. In patients with urogenital complaints external urethral or anal sphincter EMG frequently shows prolonged and polyphasic muscle potentials consistent with de- and reinnervation of voluntary sphincter muscles. Cranial computerized tomography (CCT) may demonstrate infratentorial atrophy in MSA patients, however, the diagnostic sensitivity is unsatisfactory. In up to 90% of MSA patients MRI reveals typical changes in the striatum, brain stem and cerebellum. In T2 weighted images there is frequently a hyperintense band-like signal adjacent to the posterior lateral putamen. Such increased signal intensity may correspond to activated microglia and is frequently associated with putaminal atrophy and/or hypointensity. The hyperintense periputaminal signal has recently been confirmed as useful diagnostic marker with a sensitivity of 93% as well as specificity of 88%. Hyperintense T2 signal changes are also frequently present in the pons ("hot cross bun" sign). Atrophy-related changes of basal ganglia, brain stem and cerebellum have recently been quantified in patients with parkinsonian disorders using MR volumetry (MRV). The results suggest that, at group level, patients with MSA-P and PSP can be distinguished from those with PD using MRV. Whether MRV improves diagnostic accuracy in individual patients with possible MSA remains to be shown. MR spectroscopy of the lentiform nucleus has been performed in a number of MSA patients revealing reduced N-acetylaspartate as a metabolic correlate of neuronal cell loss. Further studies are required to establish whether MRS is more sensitive to detect striatal pathology in MSA patients compared to conventional MRI.
Functional imaging with SPECT may be helpful in patients with questionable MSA (see table). IBZM SPECT consistently shows reduced striatal dopamine D2 receptor binding in MSA patients. Schwarz and colleagues were able to show that a reduction in striatal IBZM binding predicted unresponsivness to L-dopa in their patients with untreated de-novo parkinsonism. Most of these patients either developed MSA-P or PSP. In contrast, SPECT invesigations using dopamine transporter ligands such as betaCIT appear to be unhelpful in the diagnosis of patients with possible MSA. PET can also contribute to the early diagnosis of MSA, but it is still not widely available.
SPECT and PET Findings in MSA
| Ligand | Binding | Findings |
SPECT | 123I-Beta-CIT | DAT | reduced striatal DAT-function |
| 123I-IBZM | D2 Receptor | reduced striatal binding |
PET | 18F-DG | Glucose | striato-frontal hypometabolism, brainstem/cerebellum hypometabolism |
| 18F-DOPA | DDC-Activity | reduced in putamen and caudate nucleus |
| 11C- DTBZ | VMT-2 | reduced striatal VMT-2 function |
| 11C-SCH23390 | D1 Receptor | reduced striatal binding |
| 11C-Raclopride | D2 Receptor | reduced striatal binding |
| 11C-Diprenorphine | Opioid receptor | reduced in putamen and caudate nucleus |
Beta CIT, 3-beta-(4-iodophenyl)tropane-2beta-carboxylic acid; DAT, Dopamine transporter; DDC, Dopa-Decarboxylase; DTBZ, dihydrotetrabenazine; FDG, 2-18F fluoro-2-deoxy-D-glucose; IBZM, 2-hydroxy-3-iodo-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl] benzamide; NMSP, N-methylspiperone; PET, positron emission tomography; SPECT, single photon emission computerized tomography; VMT, vesicular monoamine transporter