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Dolor Neurític en Expedicions

NEUROPATHIC PAIN AFTER HIMALAYAN EXPEDITIONS.

Antoni Ricart de Mesones, MD; Janina Turón Sans, MD;  Mercedes Misiego, MD; Hisao Onaga Pueyo, MD; Rosa Real Soriano, MD; and Javier Botella de Maglia, MD.

From the Mountain Medicine Studies Institute Dr. Castelló Roca (IEMM), (Drs. A. Ricart de Mesones, H. Onaga Pueyo, and J. Botella de Maglia), the Spanish Society for Mountain Medicine (Drs. A. Ricart de Mesones, R. Real Soriano, and J. Botella de Maglia); and the Department of Neurology, Bellvitge University Hospital, Barcelona (Dr. J. Turón Sans).

Abstract 
High-altitude peripheral nerve disease secondary to frostbite or trauma is a well-recognized medical problem during mountaineering expeditions. However, in our experience of medical professionals on 19 expeditions to the Himalayas in the years 1977–2000, an unusual syndrome of neuropathic pain and/or dysesthesia in both feet apparently unrelated to frostbite or trench foot was observed in 8 (4.8%) of 165 European mountaineers. Mountaineers complained of persistent and continuous pain, which was consistently described as a ‘corky feeling’ sensation in their feet, associated with severe lancinating exacerbations. Pain improved with cold and worsened with heat and gentle pressure. Symptoms were incapacitating in a third of cases. Treatment with carbamazepine was effective and the disorder evolved to total resolution in 4–8 weeks. We present the case of a patient who had this syndrome and in whom complete work-up studies done on his arrival home, 14 days after its presentation, were unrevealing. The paucity of information regarding this particular variety of neuropathic pain of the feet may be due to lack of clinical suspicion in the field, favorable outcome, and difficulties for further study and evaluation.

Introduction
Some physicians with large experience in high-altitude expeditions are familiar with a clinical condition characterized by unexplained pain and dysesthesia in both feet during expeditions to Himalaya or Karakoram. Although this particular variety of neuropathic pain without any visible injury of the tissues, apparently unrelated to frostbite, known trauma or trench foot, has previously been reported in non-English language journals (Villas et al, 1982, 1984; Ricart de Mesones, 1994, 2000; Turón et al, 2000; Real et al, 2001), language barriers prevented accessibility of the incidence, clinical features, and prognosis of this medical illness to the international literature. This case report of a patient who has recently been studied and followed up by our group illustrates several characteristics of neuropathic pain of the feet in European mountaineers.

Case:
A group of three mountaineers opened a new route in the North Face of Amin Brakk (5,850 m) in Karakoram. The climb was extremely difficult (A5/6ºc+/60º), long (1,650 m), humid, and moderately cold. A duration of 27 days was foreseen but the climb took 5 days more; therefore, water and food were rationed. The mean temperature was 0ºC and the equipment was the appropriate for a climb of these characteristics. When returned to the base camp at 4,600 m, a 37-year-old man suffered from pain and dysesthesia in the soles and toes, slightly more severe on the left foot. Pain was intense and continuous with acute burning exacerbations accompanied by bradycardia and diaphoresis. It improved with cold and worsened with warmth inside the sleeping bag. Painful areas showed a sock-like distribution in both feet with distal predominance. There was a decrease of epicritic sensitivity, which was described by the patient as ‘corky toes’. Pain was elicited by minor contacts, e.g. the smooth contact of bedclothes. The patient feared to have suffered from frostbite but he could not remember when or how could he have had their feet frostbitten. Five days later, he consulted with two of the authors who at this time were taking part in another expedition (Real et al, 2001). The patient was treated with carbamazepine, 200 mg every 8 hours, and marked relief of pain was obtained. On his arrival home, 14 days after his initial presentation, he was studied in our hospital.
On admission the patient had dysesthesia and pain in both feet. The pain intensity was 2 in a scale from 0 to 10 (it had been 8 at the beginning of the illness). The map of the sensitive dysfunction is shown in Figures 1 and 2. No motor deficits or impairment of patellar or Achilles tendon reflexes were observed. The skin temperature, color, and morphological appearance of the lower extremities were normal (the consultation room temperature was 22ºC). There were no visible lesions suggesting frostbite, inflammation or ischemia. Physical examination of pulses and circulation of the extremities were normal. Neither passive nor active movements of the joints produced pain but blunt or rubbing contact to the skin evoked a painful feeling. When the patient’s feet were exposed to cold, toes became cyanotic suggesting intense vasoconstriction and the patient referred pain improvement. By contrast, hyperemia and pain were related to warmth. Conventional sensitive electroneurography was normal, as well as the quantitative thermotest (analysis of thresholds for cold, heat, and pain induced by cold and heat). Laboratory tests were unrevealing except for hepatic dysfunction, which was attributed to treatment with carbamazepine, and a subclinical hypothyroidism. However, thyroid function tests returned to normal values without treatment and liver function tests normalized after withdrawal of carbamazepine treatment. Invasive studies such as neural and muscle biopsies were not indicated because of the favorable patient’s clinical course with complete disappearance of signs and symptoms after 5 weeks.

Epidemiological data
In our experience of medical professionals on 19 expeditions to the Himalayas in the years 1977–2000, a syndrome of neuropathic pain and dysesthesia in both feet, without any clinical sign of tissue injury due to cold, “immersion or trench foot” or trauma was observed in 8 (4.8%) of 165 European mountaineers (Table 1). Some of the 165 mountaineers suffered from frostbite or different kinds of tissue injuries. Neuropathic troubles related to any kind of visible tissue injury, frostbite or trench foot were excluded of the table.
No Hunza, Balti, Sherpa or Tibetan high-altitude porters consulted during the expedition for pain or dysesthesia related to this syndrome. 
In all cases, the pain or dysesthesia appeared during descent to the base camp after a stay longer than two weeks climbing at altitudes above 6,000 m except in the case of the Amin Brakk and Manaslu. In all cases, mountaineers were well acclimatized and in good physical condition. In five cases the climbers were coming back from an eight thousand meters summit, or attempt to summit. Two cases appeared in mountaineers after some fruitless days waiting in a high camp due to bad weather; so, soft socks were used inside the tents much longer than hard boots or crampons. 
Motor deficit, propioceptive disturbances or dificulties for walking (except severe pain) were never seen. 
The disorder disappeared progressively over 4–8 weeks, seemingly without sequelae. Most affected mountaineers have not suffered from relapses even in later expeditions and similar conditions. In one case, pain lasted several months and became more intense when the subject came back from several hours of mountain activities, with no relation to cold. Neuralgia was severe and incapacitating only in three cases. The remaining five mountaineers could walk along the descent march. Analgesic treatment brought about a transient improvement of pain. Treatment with acetylsalicylic acid, non-steroidal antiinflamatory drugs or vitamin B did not improve the pain. In all cases pain disappeared before resolution of dysesthesia. Two subjects treated with carbamazepine showed clear improvement of symptoms, but the effect of this drug on the time-course of the disease is unknown.

Table. Occurrence of neuropathic pain among 165 European mountaineers.
The table includes only the neuropathic nuisances with normal skin (except vasoconstriction with cold and hyperemia with warmth). Neuropathic troubles related to frostbite, trench foot or trauma were excluded of the table.


Figures 1 and 2: Limits of dysesthesia for sense of touch (black) and thermal (cold) sense (white).


Discussion
In the early 80s, a series was reported of 12 mountaineers who consistently suffered from a loss of sensitivity in their toes without cutaneous signs of frostbite. All patients had taken part in long (11–63 hour) snow-and-ice climbs at high (but not extreme) altitudes (2,500–4,808 m). All cases presented with a ‘corky’ sensation and a reduction of the tactile and thermoalgesic sensitivity, which was not accompanied by skin paleness, cyanosis, blisters or pain. This disorder resolved spontaneously in 1–3 months without sequelae. The authors attributed this syndrome to the combined effect of cold, compression by the crampon straps and repeated microtrauma during snow-and-ice climbing, which could alter the toe irrigation and cause ischemic damage of digital collateral nerves. They proposed the term of ‘resolutive temporal hypoesthesia’ (Villas et al, 1981, 1982, 1984; Jimeno et al, 1981).
The syndrome here reported has some clinical similarities but the causative circumstances seem to be different.
At the present time, the pathogenetic mechanism of the syndrome is unknown. The lack of any visible injury makes hard to support the diagnosis of frostbite, trench foot or trauma. The clinical features of the pain point toward the neuropathic origin of the disorder, which is further supported by the patients clinical improvement with carbamazepine, a drug which blocks sodium channels. The fact that the syndrome is only seen in the lower extremities points out to some factor related to the longer axons. The pressure neuropathy, as suggested in the first paragraph, can not be excluded as a trigger or worsening factor, but the different circumstances of the presentation and the lack of motor or propioceptive affectation points out to small fiber polyneuropathy.
This small fiber polyneuropathy reminds the ABC syndrome (Angry Backfiring C-nociceptor), erythromelalgia or erythralgia, characterized by a warm, red limb which is hyperalgesic to heat (Cline et al, 1989; Culp et al, 1989; Campero et al, 1996; Layzer, 2001). Microvascular arteriovenous shunting and/or changes in the threshold for pain of the unmyelinated C polymodal nociceptors have been shown to play a role in the pathogenetic mechanism of this condition (Yarnitsky, 1990; Mork, 2000). On the other hand, the syndrome has been associated to different disorders including among others diabetes mellitus, metabolic or nutritional deficiencies, hematologic diseases, amyloidosis, intoxications, AIDS, and infection. All the common causes of this type of polyneuropathies must be considered, but most of these factors can be easily excluded in young healthy mountaineers. It should be noted that the majority of small caliber nerve fiber polyneuropathies are of unknown cause.
The etiology of this disorder should probably be sought among metabolic or nutritional problems, cold or altitude effects, perhaps worsened by hemoconcentration, local pressure or other factors. If nutrition, altitude or pressure were the unique etiology of the dysfunction, it would be expected for the symptoms to appear during the stay at high altitude. But in all cases symptoms appeared during or few hours after the descent. This fact suggests that some factors, maybe cold, might mask the appearance of symptoms at high altitude, since patients referred pain relief in contact with cold. The syndrome classification of these patients is essential in order to define the pathophysiology and to lead to a correct prevention and treatment. But, if the etiology is unknown and the cause no longer acts, the treatment can only be symptomatic. In the case here reported, the main symptom was neuropathic pain that responded to treatment with carbamazepine. Diagnosis on the field is based on clinical features, but specific diagnostic techniques for assessing small caliber nerve fiber neuropathy are required to confirm the diagnosis because, in these patients, results of standard tests are usually unrevealing.


References  
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