The neurosurgical subset of fibromyalgia: Part II: Radiological observations—patients vs. controls..
Michael J. Rosner, Jorge Flechas, Royce K. Bailey
Introduction: Clinical observations suggest the upper spinal cord and brainstem may be involved in a subset of patients with FM like symptoms. Objective: Test the hypothesis that there will be radiological differences related to the posterior fossa and/or cervical canal between control and the surgical subset of FMS patients. Methods: 37 patients carrying the diagnosis of ‘fibromyalgia’ were selected based upon an abnormal tilt table examination defining cardiovascular/autonomic dysfunction (NMH/POTS) 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; cerebrospinal 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, vertebral artery 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 used for data analysis; all values X + SD.
Conclusion: FM-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. INTRODUCTION: We have observed subtle radiographic changes on craniocervical MR scans of patients with neurological findings related to the brainstem and upper cervical spinal cord sufficient to explain clinical symptoms and physical findings. However, in most cases, these MR scans were reasonably read as “normal” by radiologists, leading the referring physician to seek other than structural etiologies for the patient’s complaints. This is an important error not to make, and we wish to establish a set of observations which might provide a core of information to help make an accurate radiological diagnosis in this group of patients. HYPOTHESES: The cerebellar tonsils will be lower in FMS patients when compared with controls. Similar hypotheses will be tested for differences between FMS 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 (FMS) and who had also had a tilt table test positive for neurally mediated hypotension (NMH) and/or positional orthostatic tachycardia syndrome (POTS). Assessments were recorded on a data sheet which included:
Distance above or below the lower limit of the foramen magnum (in mm) for the:
____ Midline Tonsil
____ Left paramedian tonsil
Relation of the upper cervical cord and/or medulla to the vertebral arteries:
Right ____ 0 = “CSF” signal completely separates cord from vertebral artery
Relationship of cerebellar tonsils within foramen magnum (transaxial views):
0 = No tonsil in foramen magnum
Measurements (in mm) of the cervical cord at C2 through C7: These measurements were made perpendicularly 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:
Tonsil Relation to Foramen Magnum
Tonsil-Right (mm) 3.6 ± 3.9 0.86 ± 2.9 0.010 YES
Tonsil-Left (mm) 3.3 ± 3.7 0.50 ± 2.4 0.008 YES
Tonsil-Midline (mm) 2.9 ± 3.9 -1.0 ± 4.2 0.005 YES
Impaction in FM 2.5 ± 1.0 1.2 ± 1.1 0.002 YES
VA impaction brainstem
Right Vertebral 1.1 ± 0.8 0.6 ± 0.9 0.170 NO
Left Vertebral 1.2 ± 0.7 0.3 ± 0.6 0.0002 YES
C1 Canal (mm) 15.1 ± 1.7 16.5 ± 1.5 0.045 YES
C2 Canal (mm) 11.7 ± 1.7 13.0 ± 1.5 0.001 YES
C3 Canal (mm) 11.1 ± 1.7 13.0 ± 1.5 0.001 YES
C4 Canal (mm) 10.8 ± 2.2 13.1 ± 1.8 0.002 YES
C5 Canal (mm) 10.6 ± 2.4 11.9 ± 1.6 0.068 ?
C6 Canal (mm) 11.5 ± 2.0 11.8 ± 1.2 0.597 NO
C7 Canal (mm) 13.5 ± 1.7 13.6 ± 1.0 0.768 NO
* All ‘p’ values ‘two-tailed’, separate variance
Adequate control data did not exist to compare other aspects of the scans between the two groups. However, the scan of the FMS-NMH/POTS patient typically will show:
Poor to absent CSF circulation posterior to the cerebellum
DISCUSSION: The cerebellar tonsils in FMS-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
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.
To identify surgical candidates by screening MR scans of the neck and posterior fossa independently of the neurological history and examination.
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