INTRODUCTION: Neurally mediated hypotension (NMH) and positional orthostatic tachycardia (POTS) are disabling dysautonomias which involve the cardiovascular system. Treatment has been symptomatic and centered about volume expansion, sympathomimetics and beta-blockade; however, there has been no cure and the disease is often slowly progressive.(3) Diagnosis is based upon index of suspicion but is often delayed due to the vague nature and large number of complaints which accompany the syndrome.(2) Tilt table testing is diagnostic with the demonstration of >10 mm Hg decrease in mean arterial pressure with induced tachycardia. We have previously reported that the symptoms of NMH and POTS in those with a positive tilt table examination, when accompanied by neurological deficits related to the brainstem, may be ameliorated by posterior fossa decompression in parallel with symptoms more traditionally related to brainstem compression and Chiari syndrome.(6,8) However, while neurological deficits and symptoms improved, no data have yet been presented to show that the results of a positive tilt table examination return toward normal after posterior fossa decompression. HYPOTHESIS: Induced tachycardia would result in lesser changes in MAP one year after posterior fossa decompression than the pre-operative decrease. METHODS: Eighteen patients with abnormal tilt table examinations prospectively underwent serial neurological examinations, completed protocol questionnaires detailing symptoms, and at one year after surgery, underwent repeat tilt table examinations. All tilt table examinations were accomplished by a cardiologist (RKB). Tachycardia was induced using dobutamine 1 mg/cc or isoproterenol 0.02 mg/cc and titrated to 85% of the maximum predicted heart rate or as tolerated. Blood pressure was recorded at the maximum heart rate achieved. The same protocols were used at one year after surgery and performed by the same cardiologist. Surgery consisted of a posterior fossa craniectomy extending approximately 2.0-2.5 cm above the foramen magnum and 2.0-2.5 cm to either side of the midline. Bovine pericardium was used for a duraplasty in each case. The ring of C1 was removed in each case and upper cervical laminectomy was performed when and if the spinal cord was significantly distorted. Tonsillectomy was carried out in sub-pial fashion to the point that the IX, X, XI nerves were decompressed at the point of exit, branches of PICA were allowed to move away from the brainstem and neuromas of the XI nerves were freed from the dentate ligaments. RESULTS: At one year after surgery there were slight but statistically insignificant increases in resting heart rate, systolic, diastolic and mean blood pressures. However, tachycardia precipitated a 41 mmHg systolic drop before surgery (table 1), but only 3 mmHg 12 months afterward (p=0.00005, t-test, unpaired, unequal variances). Diastolic pressure dropped 31 mmHg prior to surgery and by only 13 mmHg post-operatively (p=0.0001); mean blood pressure decremented by 38 mmHg before surgery, but only 10 mmHg afterward (p=0.0002). By 12 months, 14 TTT were completely negative, 3 were still positive but improved, and one was only slightly improved. The latter four patients accounted for nearly all of the net declines in SBP, DBP, and MAP. Similarly, symptoms (table 2) such as palpitations, dizziness, chest pain, shortness of breath (SOB), syncope and presyncope improved markedly as they had in previous reports.(6,8) All neurological examinations were abnormal at intake with both cranial nerve deficits and long tract abnormalities. Cranial nerve deficits improved over baseline conditions (*table 3, p=0.016) as did long tract abnormalities (**table 4, p=0.008). While still present even one year after surgery, improvement was often continuing and had not yet reached a plateau in most subjects. Deficits, even though still present, were usually quantitatively improved which is not apparent from these tables. This series includes data from those who have had subpial resection of their tonsils as part of their surgical treatment. There were three patients who had had only suboccipital craniectomy with duraplasty who remained symptomatic and had persistently positive tilt table examinations. These converted to negative in two cases and markedly improved in a third. Figure 1-2 demonstrate the pre- and post-operative MR scans done in three planes in one such patient. Table 1: Pre- vs. post-operative blood pressure response to induced tachycardia (x ± sd, [median])

Table 1: Pre- vs. post-operative blood preasure response to induced tachycardia (x +/- sd. [median]

T-test, two group, unequal variances assumed; p values one-tailed

Table 2: Cardiovascular Symptoms

*Less frequent, less severe in one; unchanged in one.

Discussion: The symptoms and signs of Chiari Malformation or, better, the hypoplastic or dysplastic posterior fossa, are numerous and wide ranging. (4,7,9) Lower cranial nerve deficits, nystagmus and ataxia are well recognized symptoms and signs of Chiari, but few are aware of the multiple dysautonomias which may also result from lower brainstem and upper cervical cord compression.  These dysautonomias include gastroesophageal reflux, irritable bowel syndrome, urogenital dysfunction as well as NMH and POTS.(7,9) This study has focused on these cardiovascular dysautonomias because the tilt table evaluation offers an objective measure of the degree of dysautonomia and can be repeated to assess the results of surgical therapy.  In addition, since many patients with multiple complaints (“positive review of symptoms”) may be dismissed as being of psychosomatic origin, the tilt table test offers objective evidence of disease—it cannot be faked or exaggerated—and a physiological reason for multiple complaints should be sought. The brainstem and upper cervical cord are perfectly capable of causing a plethora of superficially “weird” complaints. Not only can the clinical picture be confusing, but the radiological criteria of Chiari have changed drastically and many patients symptomatic from a hypoplastic or dysplastic posterior fossa have little or no tonsillar herniation.(4,7,9) However, they often demonstrate abnormal boney morphology(4), invagination of the brainstem by the vertebral arteries, tonsillar asymmetry with brainstem shift and other findings.(9) The importance identifying these patients lies in their outcome following decompression of the brainstem.  Subjective and functional impairments improve substantially.  Not only do the cardiovascular symptoms and tachycardia induced hypotension improve as demonstrated in this study, but the vast majority of apparently unrelated symptoms including pain also improve.(1,5,6)  By one year after surgery, employment has increased from 25% to 75%, narcotic and other drug use observations suggest improvement may continue for 24-36 months and perhaps longer and may be prominent in even the most severely affected patients. In addition, the failure of simple decompression in a number of cases which led to re-operation and tonsillectomy suggests that at least by this measure, more complete decompression of the brainstem may be required than is achieved by craniectomy and duraplasty which only decompresses the posterior aspect of the brainstem. Ongoing analysis suggests the antero-lateral decompression achieved by sub-pial tonsillectomy provides a better functional result.
Conclusions:
1. Neurally Mediated Hypotension, Positional Orthostatic Hypotension and Tachycardia Induced Hypotension may be:
        a. Caused by brainstem and upper cervical cord compression due to Chiari Syndrome.
      b. Significantly improved or even cured by posterior fossa decompression.
2.    Are associated with other symptoms and signs of Brainstem compression (Chiari syndrome) which improve in parallel with NMH and POTS.
3.    Can be objectively diagnosed by a Cardiologist administered tilt table examination.

References:
1.    Flechas J and Rosner MJ: Neurosurgical subsets of fibromyalgia: Part IV: Long term outcome as measured by dolorimetry. J Musculoskeletal Pain 9 (S5):29, 2001.

2.  Goldstein DS: Mysterious or Controversial Entities, in Goldstein DS (ed): The Autonomic Nervous System in Health and Disease. New York, Marcel Dekker, Inc., 2001, pp 525-573.

3.    Goldstein DS: The Autonomic Nervous System in Health and Disease. New York, Marcel Dekker, Inc., 2001.

4.  Milhorat TH, Chou MW, Trinidad EM, Kula RW, Mandell M, Wolpert C, and Speer MC: Chiari I Malformation Redefined: Clinical and radiographic findings for 364 symptomatic patients. Neurosurgery 44:1005-1017, 1999

5.  Munis JR and Lozada LJ: Giraffes, siphons, and starling resistors. Cerebral perfusion pressure revisited. [letter; comment.]. Journal of Neurosurgical Anesthesiology 12:290-296, 2000.

6.  Rosner, M. J., Flechas, J., and Bailey, R. K. Neurally Mediated Hypotension (NMH) and Positional Orthostatic Tachycardia Syndrome (POTS): Part III: Symptomatic and functional outcome one-year after surgery. Poster Program: AANS 2002. 2002.

7.  Rosner MJ, Flechas J, and Bailey RK: Neurosurgical subsets of fibromyalgia: Part II: Radiological observations versus control subjects. J Musculoskeletal Pain 9 (S5):31, 2001.

8.  Rosner MJ, Flechas J, and Bailey RK: Neurosurgical subsets of fibromyalgia: Part III: Functional and symptomatic outcome at 12 months postopperatively. J Musculoskeletal Pain 9 (S5):32, 2001.

9.  Rosner, M. J., Flechas, J., and Bailey, R. K. Neurally Mediated Hypotension (NMH) and Positional Orthostatic Tachycardia Syndrome (POTS): Part II: Radiological observations--patients vs. controls. Poster Program: AANS 2002. 2002.

Acknowledgement: This work supported in part by a grant from Dr. John Edwards and the Park Ridge Hospital Foundation 

*Table 3:  Cranial nerve abnormality pre-vs.post-operatively (p=0.016, sign test)

*Table 4: “Long tract” neurological abnormalities (p=0.008, sign test)

Abstract presented at                          
Congress of                             
Neurological Surgeons                       
Annual Meeting – 2003