Sympathetically maintained pain: has the emperor no clothes?

Acute response to intracisternal bupivacaine in patients with refractory pain of the head and neck

Continuous intracisternal infusion of bupivacaine for the management of intractable pain of the head and neck is effective in controlling pain in this patient group. With the catheter tip being located at the height of the C1 vertebral body, autonomic regulatory information may also be influenced by the infusion of bupivacaine. By combining direct sampling of cerebrospinal fluid (CSF), via a percutaneously placed catheter in the cisterna magna, with a noradrenaline and adrenaline isotope dilution method for examining sympathetic and adrenal medullary activity, we were able to quantify the release of brain neurotransmitters and examine efferent sympathetic nervous outflow in patients following intracisternal administration of bupivacaine. Despite severe pain, sympathetic and adrenal medullary activities were well within normal range (4.2 +/- 0.6 and 0.7 +/- 0.2 nmol min(-1), respectively, mean +/-S.E.M.). Intracisternal bupivacaine administration caused an almost instantaneous elevation in mean arterial blood pressure, increasing by 17 +/- 7 mmHg after 10 min (P < 0.01). Heart rate increased in parallel (17 +/- 5 beats min(-1)), and these changes coincided with an increase in sympathetic nervous activity, peaking with an approximately 50% increase over resting level 10 min after injection (P < 0.01). CSF levels of GABA were reduced following bupivacaine (P < 0.05). CSF catecholamines and serotonin, and EEG, remained unaffected. These results show that acutely administered bupivacaine in the cisterna magna of chronic pain sufferers leads to an activation of the sympathetic nervous system. The results suggest that the haemodynamic consequences occur as a result of interference with the neuronal circuitry in the brainstem. Although these effects are transient, they warrant caution at the induction of intracisternal local anaesthesia.

Chronic pain: physiological, diagnostic, and management considerations

Neuropathic pain is a neuropsychiatric condition in which pain is initiated or caused by a primary lesion or dysfunction in the nervous system. Understanding the complexity of neuropathic pain becomes the cornerstone for appropriate diagnosis and management. Diagnosis must take into account comorbid conditions. Successful management depends on realistic patient and physician expectations and an individualized, multidisciplinary approach.

Reflex sympathetic dystrophy: misdiagnosis in patients with dysfunctional postures of the upper extremity

The purpose of this case-control study was to assess the frequency of the inappropriate diagnosis of reflex sympathetic dystrophy (RSD) in patients who presented with dysfunctional postures of the upper extremity (n = 43). This group of patients with a dysfunctional posture was compared with a randomly selected control group of patients who presented with pain but no dysfunctional posture (n = 88). The patients underwent radiographic evaluation after review of previous medical records and history and physical examination. Patients with dysfunctional postures had a significantly higher frequency (63%) of a previous inappropriate diagnosis of RSD compared with the control group (6%). None of the patients in either group had objective findings consistent with a diagnosis of RSD. Patients presenting with dysfunctional postures of the upper extremity may be misdiagnosed as having RSD and rarely meet the criteria for this diagnosis.

Abnormal movements in complex regional pain syndrome: assessment of their nature

Abnormal movements may be a clinical feature in complex regional pain syndrome (CRPS), but their basic nature is unclear. Between August 1989 and September 1998, patients fulfilling diagnostic criteria for CRPS (I or II) and displaying abnormal movements were entered into a prospective study. Fifty-eight patients, 39 women and 19 men, met entry criteria; 47 had sustained a minor physical injury at work. The patients exhibited various combinations of dystonic spasms, coarse postural or action tremor, irregular jerks, and, in one case, choreiform movements. Patients underwent rigorous clinical and laboratory evaluation aimed at characterizing their neurological disturbance. Surprisingly, no case of CRPS II but only cases of CRPS type I displayed abnormal movements. In addition to an absence of evidence of structural nerve, spinal cord, or intracranial damage, all CRPS I patients with abnormal movements typically exhibited pseudoneurological (nonorganic) signs. In some cases, malingering was documented by secret surveillance. This study highlights abnormal movements in CRPS as constituting a key clinical feature that differentiates CRPS I from CRPS II. They are consistently of somatoform or malingered origin, signaling an underlying psychoneurological disorder responsible for the entire CRPS profile.

Does sympathetic nerve discharge affect the firing of polymodal C-fibre afferents in humans?

Experimental and clinical studies in animals and humans have indicated that nociceptive nerve fibres can acquire sensitivity to norepinephrine after injury or chemical sensitization. To evaluate the functional relevance of such sensitization, we recorded the activity of single polymodal C-fibre afferents in healthy human volunteers and investigated whether intense physiological sympatho-excitation could affect their firing properties. This was studied before and after chemical sensitization of receptive fields by topical application of mustard oil. All afferent C fibres investigated (11 units in 10 subjects) were mechano-heat-sensitive, and four of seven fibres subjected to mustard oil were also chemosensitive. Putative sensitivity to sympathetic stimulation was investigated during low-frequency (0.25 Hz) electrical stimulation of the unit receptive field at a threshold intensity sufficient to evoke an action potential in the afferent fibre after every second to third stimulus. Following a prolonged period of silent rest, sympathoexcitation was elicited by forced mental arithmetic for 60 s, again followed by a long silent rest period. During stress, sympathetic nerve traffic increased to 625 +/- 146% of the control level, while firing of the afferent units remained unchanged. There was no sign of sympathetically mediated direct activation of afferent units and no change in the relative amounts of afferent activations caused by the background electrical stimulation. Results were similar for all units, both before (seven units in six subjects) and after (seven units in seven subjects) chemical sensitization of their cutaneous receptive field. The results suggest that if chemical sensitization of nociceptive C afferent neurons with mustard oil does induce sensitivity to noradrenaline in humans, it is not sufficient to make C nociceptive fibres respond to short-lasting physiological variations in sympathetic outflow.