On the water's edge

Rock-a-bye paralysis

MJA 1997; 167: 632  

The soporific benefits of waterbeds have been known for thousands of years, since Persian nomads first slumbered on sun-warmed goatskin waterbags. Cleopatra is said to have slept on a waterbed, and Leonardo da Vinci sketched designs for their construction. Their therapeutic value was championed by Neil Arnott in 1833, who visualised the ideal state of "repose on the surface of the water, like a swan on its plumage, without sensible pressure anywhere".1 In the late 1960s, waterbeds became commercially available, and they were soon popular for both restful and romantic reasons. There appear to have been few complaints on either score. However, some inherent perils deserve to be highlighted. I report three patients for whom sleeping on a waterbed was associated with the development of compression palsy of the common peroneal nerve.   Clinical record Case one: A 45-year-old truck driver, with an unremarkable previous medical history, woke one Sunday morning "unable to walk". His wife described him, intoxicated after a Christmas party the night before, flopping into their waterbed with his legs lying across the edge of the bed for most of the night. On examination, he had a significant foot drop, owing to a left common peroneal nerve palsy. There was tenderness over the nerve at the level of the head of fibula. He was managed symptomatically and made a good functional recovery in five days, although reporting a "weak ankle" persisting for some weeks. Case two: A 55-year-old man with well controlled diabetes, with no history of neuropathy, retinopathy or nephropathy, woke on a Sunday morning alongside his wife and stumbled out of bed "unable to walk properly". He denied any alcohol intake the previous evening but had had "an uncomfortable night's sleep". On examination, he had a left common peroneal nerve palsy. Nerve conduction studies demonstrated a focal conduction block in the common peroneal nerve but no evidence of generalised peripheral neuropathy. At six months, he still has a "weak ankle" but has little evidence of a foot drop. Case three: A 33-year-old male physician woke with a "dead foot" after sharing a "smallish waterbed" with his partner one Saturday night. He had taken a small amount of alcohol before going to bed and had enjoyed a good night's rest. On examination, he had a right common peroneal nerve palsy, which symptomatically resolved over five days with no subjective residual ankle weakness. The physician and his partner are now married and have bought a conventional bed.   Discussion There have been few documented medical complications arising from waterbed use. I found only four reports of complications (in the 61 articles published between 1966 and August 1997, accessed through MEDLINE, that include "waterbed" as a text word). Both hypothermia and hyperthermia have been described, the latter caused by an elevated heater setting on a waterbed and initially thought to be a nosocomial fever.2,3 In another case, a leaking waterbed mimicked prematurely ruptured fetal membranes.4 Other case descriptions have implicated waterbeds in the sudden death of some infants.5 There is no evidence that waterbeds cause seasickness or lead to increased gastro-oesophageal reflux.6 All three patients reported here had slept on waterbeds with a rigid "wooden-box" frame. It is likely that the firm edge of the bed contributed to their focal compression palsy. All had slept with a partner and developed weakness in the leg on the side of the bed that they normally slept on. It is possible that as a person rolls towards the middle of the bed and their body sinks, the near leg rides up and over the firm edge. Further "tidal movement" by the person or their partner damages the nerve at the fulcrum. Alternatively, if the legs are crossed on a waterbed, the weight of the top leg may push the near leg under and across into the submerged edge. Peroneal nerve palsy is usually caused by external compression, and may be seen after anaesthesia, intoxication, coma or prolonged bed rest. Many case reports, however, give no clear history of compression. The nerve palsy is often ascribed to abnormal sleep postures, as symptoms are usually first noticed on awakening.7 It is not clear how many of these patients may have slept on waterbeds. The intoxication in the first patient described here and the Sunday-morning onset in all three patients suggest similarities with compression neuropathy of the radial nerve (so-called "Saturday-night palsy"). Waterbeds certainly have benefits in some circumstances but we have every reason to be apprehensive about the cutting edge of technology. For, despite the evolution of "soft edge models", we have not yet realised Neil Arnott's ambitious hopes of slumber "without sensible pressure". Until we do, peroneal nerve palsy will continue to remain a matter of gravity. Merlin C Thomas Senior Registrar, Department of Medicine University of Otago, Dunedin, New Zealand E-mail: mdorbell AT es.co.nz Arnott N. Elements of physics or natural philosophy, vol 1. London: Longman, Rees, Orme, Brown and Green, 1833. Gonzalez EB, Suareze L, Magee S. Nosocomial (water bed) fever. Arch Intern Med 1990; 150: 687. Jones RF, Hatzidoulis C, Chestnutt U, Stewart L. The "Coast" hydrostatic bed. Med J Aust 1975; 1: 333-335. Merritt D. Leaking waterbed mimicking prematurely ruptured foetal membranes. New Engl J Med 1991; 324: 274. Ponsonby AL, Lyons TJ, Dwyer T, Carmichael A. Free-flow waterbeds are potentially dangerous to infants [letter]. Med J Aust 1995; 162: 391-392. Wang JC, Castell DU, Sinclair JW, Wu WC. Does sleeping on a waterbed promote gasto-oesophageal reflux? Dig Dis Sci 1989; 34: 1585. Berry H, Richardson PM. Common peroneal palsy: a clinical and electrophysiological review. J Neurol Neurosurg Psychiatry 1976; 39: 1162-1171.