Introduction: Clinical observations suggest the upper spinal cord and brainstem may be involved in a subset of patients with symptoms related to NMH/POTS. Objective: Test the hypothesis that there will be radiological differences related to the posterior fossa and/or cervical canal between control and those patients with NMH/POTS. Methods: 37 patients were selected based upon an abnormal tilt table examination defining cardiovascular/autonomic dysfunction and abnormalities identified from the neurological examination. Protocol magnetic resonance (MR) scans of the craniocervical junction region were accomplished for each patient in sagittal, coronal and transaxial planes; cerecerebrospinal fluid (CSF) flow via phase contrast MR was assessed. Specific grading of tonsillar descent (midline and paramedian), obex height, tonsillar impaction within the foramen magnum (FM), vertebral artery (VA) invagination of the brainstem, and AP diameter of the foramen magnum was carried out. The spinal cord and canal diameters were measured at each disk level with electronic calipers. These results were compared with those of asymptomatic control patients. Systat 7.0 and Excel were usef for data analysis; all values X + SD.

Conclusion: NMH/POTS patients with abnormal neurological examinations represent a population that is radiographically distinct from asymptomatic individuals. These differences relate to the brainstem and cervical spinal cord as suggested by neurological examinations. However, the overlap of standard deviations is such that simple review of MR scans will not discriminate between these groups independently of the neurological exam. HYPOTHESES: The cerebellar tonsils will be lower in NMH/POTS patients when compared with controls. Similar hypotheses will be tested for differences between NMH/POTS patients and controls with regard to: tonsillar impaction into the foramen magnum, vertebral artery impaction into the brainstem, and the AP diameter of the cervical canal at each level. Hypothesis statement and testing was of the form:

H1: μ1 ≠ μ0

H0: μ1 = μ0

METHODS: Protocol MR craniocervical scans were obtained on 37 patients who carried the diagnosis of fibromyalgia syndrome and who had also had a tilt table test positive for neurally mediated hypotension and/or positional orthostatic tachycardia syndrome. Assessments were recorded on a data sheet which included: Distance above or below the lower limit of the foramen magnum (in mm) for the:

Relation of the upper cervical cord and/or medulla to the vertebral arteries:

Relationship of cerebellar tonsils within foramen magnum (transaxial views):

Measurements (in mm) of the cervical cord at C2 through C7: These measurements were made perpen- dicularly to the cord and centered at each disc space to facilitate reproduction of these same measurements on subsequent scans. These results were compared to similar measurements obtained from 40 asymptomatic control subjects previously recruited for a separate study and supported by the National Fibromyalgia Research Association. Other observations included:

Adequate control data did not exist to compare other aspects of the scans between the two groups. However, the scan of the NMH/POTS patient typically will show:

1. Poor to absent CSF circulation posterior to the cerebellum
2. Poor CSF flow posterior to the cervical cord
3. A ‘meniscus’ sign below the cerebellar tonsils
4. Distortion and subtle shift of the brainstem on transaxial views of the foramen magnum
5. Compression of the cerebellar folia in the inferior cerebellum
6. Absence of the subarachnoid space posterior to the cerebellar hemispheres
7. Others

DISCUSSION: The cerebellar tonsils in NMH/POTS patients descend further through the foramen magnum than do those of control subjects. The population difference is about 3 mm lower for the affected patients than in controls. The absolute descent is greatest for the right cerebellar tonsil, though the variability is great The tonsils typically both descend into the foramen magnum and mold to some degree about the brainstem while the typical control patient shows only minimal presence of the tonsils in the foramen magnum. This will reduce the relative CSF space within the foramen magnum and increase the pressure gradient needed to move CSF through the foramen during systole and diastole. The mid and upper cervical segments fail to enlarge to a normal degree and remain significantly narrower than in control patients. The canal from C5 rostrally is about 1.5-2.0 mm smaller than control subjects. The narrower canal and tighter foramen magnum will increase the liability of the patient to hyperextension injuries. These are particularly prominent in “whip-lash” like events, during some surgeries, falls, and some forms of forceful forward bending. The subtle nature of these differences, though real, mean that accurate diagnosis must be based upon a very thorough and critical neurological exam anatomically related to the upper spinal cord and/or brainstem (part I). Merely using the MR scan, or worse, its radiological interpretation, as a screen for the presence of compression will usually be misleading.

CONCLUSIONS: Patients with the diagnosis of NMH/POTS represent a population radiographically separate from the asymptomatic control population.

2. These relationships correspond anatomically to the neurological examination findings presented in part I.

3. The findings are in the direction of developmental cervical stenosis and/or the hypoplastic posterior fossa, either of which can be associated with compression of the brain stem and or cervical spinal cord and which are amenable to surgical decompression when symptoms are severe enough.

Abstract Presented at American Assoc of Neurological Surgeons Annual Meeting-2002.

National Fibromyalgia Research Association Neurology & New Treatment Modalities In FM Symposium –Portland, OR-Oct 2002.