Adenosine in painful legs and moving toes syndrome

Spinal-generated movement disorders: a clinical review

Spinal-generated movement disorders (SGMDs) include spinal segmental myoclonus, propriospinal myoclonus, orthostatic tremor, secondary paroxysmal dyskinesias, stiff person syndrome and its variants, movements in brain death, and painful legs-moving toes syndrome. In this paper, we review the relevant anatomy and physiology of SGMDs, characterize and demonstrate their clinical features, and present a practical approach to the diagnosis and management of these unusual disorders.

Painful legs and moving toes

The syndrome of painful legs-moving toes (PLMT) is an adult-onset, rare disorder characterized by pain, typically of a neuropathic quality, in the feet or legs, associated with writhing movements of one or more toes. It is the pain which usually brings the patient to medical attention. The syndrome may be unilateral or bilateral. Identical toe movements may occur without pain, referred to as: "painless legs-moving toes," and a similar condition affects the upper limbs: "painful arms-moving fingers." The pathophysiology of PLMT and its variants is not known but most reports suggest an association with a peripheral lesion, usually at the level of the root or nerve, though in many cases no cause is found. It has been suggested that a peripheral lesion causes aberrant input leading to "central reorganization," probably at the level of the spinal cord, and that the latter is responsible for the pain and movement. Treatment is often unsatisfactory and many drugs commonly used for neuropathic pain have been reported anecdotally to help (e.g., gabapentin). Other anecdotal therapies include spinal blocks, spinal cord stimulation, and local injection of botulinum toxin.

Case reports: Painful limbs/moving extremities: report of two cases

BACKGROUND

Painful limbs/moving extremities is a relatively rare condition characterized by aching pain in one limb and involuntary movement in the affected fingers or toes. Its pathomechanism is unknown. We report two patients with painful limbs/moving extremities. In one patient with a painful arm and moving fingers, the symptoms were resolved after surgery.

CASE DESCRIPTIONS

Patient 1 was a 36-year-old man with a painful arm and moving fingers. Treatment with administration of analgesics was not effective. Postmyelographic CT showed stenosis of the right C5/C6 foramen attributable to cervical spondylosis and a defect of the contrast material at the foramen. He was treated with cervical foraminotomy. Patient 2 was a 26-year-old woman with a painful leg and moving toes. The pain and involuntary movement appeared 2 weeks after discectomy at L5/S1. Lumbar MRI and myelography showed no indications of nerve root compression. She was treated with a lumbar nerve root block. The pain and involuntary movement completely disappeared in both patients after treatment.

LITERATURE REVIEW

Numerous studies report treatments for painful limbs/moving extremities, but few report successful treatment. Recently, botulinum toxin A injection and epidural spinal cord stimulation have been used and are thought to benefit this condition. Successful surgical treatment previously was reported for only one patient.

PURPOSES AND CLINICAL RELEVANCE

If imaging indicates compression of nerve tissue, we believe surgical decompression should be considered for patients with painful limbs/moving extremities who do not respond to nonoperative treatment.

Painful limbs/moving extremities

Painful limbs/moving extremities (PLME) is a disorder characterized by spontaneous, complex, slow (1-2 Hz) involuntary toe or finger movements. The movements that can be bilateral or unilateral are usually accompanied by pain in the affected limbs. Painless variants are less common. PLME has been associated with peripheral and central nervous system disease although idiopathic cases have been reported. Its etiopathogenesis is unknown and treatment approaches remain largely empirical. Nerve blocks and botulinum toxin type A injections as well as oral medication have had some measure of success. Current theories suggest that central oscillator(s) at the spinal or supraspinal levels may be involved. Future research in PLME should include prospective electrophysiological and functional imaging studies as well as clinical trials with botulinum toxin injections and oral pharmacological agents.

[Painful legs and moving toes syndrome]

Painful legs and moving toes syndrome is a rare medical picture characterized by involuntary movements of the toes or the whole foot and pain in lower limbs. However, this must be kept in mind due to its association with other diseases and its possibility of being the first symptom. Spinal cord and cauda equina diseases, neuropathies, radiculopathies, drugs and other systemic diseases are the main cause of this syndrome although many cases are still idiopathic. Its diagnosis is essentially clinical and its treatment is complex, including different combinations of drugs and invasive techniques, and generally with a bad response.

Pain-relieving effects of intravenous ATP in chronic intractable orofacial pain: an open-label study

PURPOSE

Chronic orofacial pain is often refractory to conventional pain therapies. We conducted an open-label study to determine whether adenosine 5'-triphosphate (ATP) could alleviate chronic intractable orofacial pain, and if so, which type of pain could respond to ATP.

METHODS

In 8 and 16 patients with non-neuropathic and neuropathic intractable orofacial pain, respectively, ATP was intravenously infused at a rate of 100 microgxkg(-1)xmin(-1) over 120 min. The magnitudes of spontaneous pain and brush-evoked allodynia were graded with a visual analog scale (VAS). When a VAS score for spontaneous pain was decreased by 50% or more by ATP, the patient was classified as a responder.

RESULTS

The patients could be clearly divided into 10 responders and 14 non-responders. Ten of the 16 patients (62.5%) with neuropathic pain, but none of the 8 patients with non-neuropathic pain, responded to ATP. In particular, all of 8 patients with neuropathic pain following pulpectomy, with or without subsequent tooth extraction, responded to ATP. In the 10 responders, VAS scores for spontaneous pain decreased slowly but progressively during the infusion period, and eventually, ATP reduced the VAS scores for spontaneous pain and allodynia by 82 +/- 15% and 74 +/- 9%, respectively. In these responders, the analgesic and anti-allodynic effects of ATP outlasted the infusion period for medians of 7 and 12 h, respectively.

CONCLUSION

Intravenous ATP did not relieve non-neuropathic orofacial pain. However, it exerted slowly expressed but long-lasting analgesic and anti-allodynic effects in patients with neuropathic orofacial pain, especially in those suffering from neuropathic pain following pulpectomy and/or tooth extraction.

Clinical application of adenosine and ATP for pain control

This review summarizes clinical application of adenosine and adenosine 5'-triphosphate (ATP) in pain conditions. Investigations have been performed in patients with acute perioperative pain or chronic neuropathic pain treated with intravenous adenosine or ATP, or intrathecal adenosine. Characteristic central adenosine A1 receptor-mediated pain-relieving effects have been observed after intravenous adenosine infusion in human inflammation/sensitization pain models and in patients with chronic neuropathic pain. Adenosine compounds, in low doses, can reduce allodynia/hyperalgesia more consistently than spontaneous pain, suggesting that these compounds affect neuronal pathophysiological mechanisms involved in central sensitization. Such pain-relieving effects, which are mostly mediated via central adenosine A1 receptor activation, have a slow onset and long duration of action, lasting usually for hours or days and occasionally for months. With acute perioperative pain, treatment with a low-dose infusion of adenosine compounds and the A1 receptor-mediated central antisensitization mechanisms may play only a minor part in the total perioperative pain experience. By administering sufficient doses of adenosine compounds during surgery, however, significant and long-lasting perioperative pain relief can be achieved via central A1 receptor-mediated antinociceptive/analgesic actions as well as via peripheral A2a or A3 receptor-mediated antiinflammatory actions. Thus, adenosine compounds have significant potential for alleviating various types of pain.

Small conductance calcium-activated K+ channels, SkCa, but not voltage-gated K+ (Kv) channels, are implicated in the antinociception induced by CGS21680, a A2A adenosine receptor agonist

It has been shown that A2A adenosine receptors are implicated in pain modulation. The precise mechanism by which activation of A2A receptors produces analgesic effects, however, remains unclear. The aim of this study was to investigate the possible involvement of apamin-sensitive calcium-activated potassium channels (SKCa) and voltage-gated potassium (Kv) channels in A2A receptor activation-induced analgesic effects. Using mice, we evaluated the influence of apamin, a non specific blocker of SKCa channels, Lei-Dab7 (an analog of scorpion Leiurotoxin), a selective blocker of SKCa2 channels, and kaliotoxin (KTX) a Kv channel blocker, on the CGS 21680 (A2A adenosine receptor agonist)-induced increases in hot plate and tail pinch latencies. All drugs were injected in mice via the intracerebroventricular route. We found that apamin and Lei-Dab7, but not KTX, reduced antinociception produced by CGS21680 on the hot plate and tail pinch tests in a dose dependent manner. Lei-Dab 7 was more potent than apamin in this regard. We conclude that SKCa but not Kv channels are implicated in CGS 21680-induced antinociception.

Sympathetic nervous system involvement in the syndrome of painful legs and moving toes

The objective of this study is to investigate sympathetic nervous system involvement in 2 patients with painful legs and moving toes. The first case was studied several years after the initiating trauma produced a peripheral nerve lesion and demonstrated the characteristic sequence of progression of pain and moving toes from the injured leg to the contralateral leg. The second case was initially studied within 3 months of an injury that did not produce definitive signs of a peripheral nerve lesion. Pain increased when the patients were startled and subsided temporarily after sympathetic blockade. In the first patient, toe movements and allodynia to light tactile stimulation persisted during sympathetic blockade, and pain sometimes returned before the vascular effects of blockade disappeared. In the second patient, pain and toe movements could be provoked reproducibly by light tactile stimulation of the affected foot and by sympathetic arousal. These symptoms and signs disappeared after lumbar sympathectomy, and re-emerged when signs of sympathetic reinnervation were detected. We concluded that sympathetic neuronal discharge may provoke pain by activating an impulse generator in the affected limb. Sympathetic involvement in the painful legs and moving toes syndrome appeared to be greater in the second case than the first, presumably due to differences in the initial injury or stage of the condition.

Treating restless legs syndrome: current pathophysiological concepts and clinical trials

Restless legs syndrome is a distinctive clinical syndrome with a prevalence of about 5% in the general population. One of the outstanding characteristics of restless legs syndrome is its extreme responsiveness to dopaminergic agents. Together with the latest pathophysiological and genetic findings, recent epidemiological and clinical data give a new insight into the classification of restless legs syndrome, thus building the theoretical foundation for the development of new pharmacological methods in its treatment. Current efforts within this area focus on establishing dopaminergic substances for therapy. The hypothesis of a disturbed iron metabolism in restless legs syndrome has been revived by recent theoretical considerations. The present review attempts to explain current strategies of treatment for restless legs syndrome in relation to aetiological, genetic and pathophysiological findings.

Syndrome of painful legs and moving toes: a case study

Painful legs and moving toes syndrome is characterized by spontaneous causalgic pain in the lower extremities associated with peculiar involuntary movements of the lower extremities, especially the toes and feet. The pain is diffuse, intractable, aching, and deep. The movements consist of persistent writhing movements in the digits that cannot be limited voluntarily. The syndrome has been observed after a variety of abnormalities affecting the posterior nerve roots, the spinal ganglia, and the peripheral nerves. This article reviews commonly reported findings and current concepts in the etiology and management of this condition.

Adenosine and the nervous system: pharmacological data and therapeutic perspectives

1. Adenosine acts on a family of G-protein-coupled receptors called purinoreceptors. 2. Four subtypes have been cloned and pharmacologically characterized. 3. The principal pharmacological data and structure-function relations for agonist interactions with P1 receptors are presented. 4. We conclude that the potent role of adenosine in the nervous system may be interesting for the development of drugs targeted at purines and their receptors.

Adenosine and migraine

BACKGROUND

Adenosine is a powerful natural vasodilator that participates in the control of cerebral and meningeal blood flow. In this context, it could be involved in the pathophysiology of migraine, since it was previously reported that intravenous adenosine can precipitate crises in migraine patients.

METHODS

We have investigated circulating adenosine levels in 12 patients suffering from migraine without aura, during crises and in crisis-free periods, and have compared the levels noted to those of a population of 10 controls. To determine if there are interactions between adenosine and serotonin, we examined the effect of adenosine and antagonists on the uptake and the release of (14C) serotonin by platelets.

RESULTS AND CONCLUSION

We have reached a dual conclusion: 1) during migraine headaches there is an increase (mean 68%) in circulating adenosine levels and this increase may participate in cephalalgia; 2) activation of A2 receptors by adenosine causes a dose-dependent serotonin uptake by platelets. This inhibition of uptake could participate in the rapid elimination of serotonin in migraine sufferers. As a result of this, the use of adenosine antagonists could be an effective complementary treatment for migraine.

Adenosine and neuropathic pain

Recent studies have reported the possibilities of relieving neuropathic pain by administering adenosine or its analogs. In order to determine if there exists a metabolic anomaly of this nucleoside in patients with neuropathic pain, circulating adenosine levels were compared in three patient groups. The first was composed of individuals suffering from neuropathic pain, the second of patients with nervous system lesions in the absence of pain, and the third was composed of patients suffering from pain resulting from excessive nociception. The adenosine blood levels of these patients were compared to those of a control group. Finally, adenosine in the cerebrospinal fluid (CSF) of some patients was also assayed. The results show that there are reduced levels of blood and CSF adenosine in patients with neuropathic pain. This adenosine deficiency could explain the potential therapeutic effects of administering adenosine or its analogs.