Pain, 6 (1979)335~347

335

© Else~er/North-Holland Biomedical Press

LONG T E ~ : I : RESULTS OF P E R ~ R ~ CONDITIONING MEASURE IN CHRONIC PAIN

MARGARETA B.E, ERIKSSON,BENGT H, SJ{3LUND* and SOEEN NIELZ~N Departments o f Clinical Neurophys~ology, Neurosurgery, Physiology and Psychiatry. University o f Lund, S.221 85 Lund (Sweden)

(Accepted February 9th, 1979)

SUMMARY In the present study 123 patients with chronic pain, consecutively referred for symptomatic pain treatment, were given peripheral conditioning stimulation as an analgesic measure and were followed for 2 years or till they terminated the treatment. The stimulation was either conventional transcutaneous nerve stimulation (TNS) [35] of mainly cutaneous afferents with high frequency (10--100 Hz) or acupuncture-like TNS [11] where muscle nerves are activated at a low repetition rate (1--4 Hz) with small trains of stimuli. The follow-up showed that 55, 41 and 31% of the patients continued the treatment after 3, 12 and 24 months, respectively. About 30% of the patients had to use acupuncture-like TNS to get useful analgesm, defined as a desire of the patient to continue stimulat':on treatment. Three-quarters of the successfully relieved patients reported more than 50% pain relief as meaese reported an increased ntake by more than 50%. for TNS treatment. It is )n is a valuable therapy in real and acupuncture-like TNS should be tried before considering implantable devices or destructive surgery.

INTRODUCTION During the last decade conditioning stimulation of peripheral nerves with ele~ric~ pulses given transcutaneously (tra~scutaneous nerve stimulation; TNS) and direct stimulation of presumably mam!~y the dorsal columns of the ....

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336 spinal cord via implanted electrodes (dorsal column stimulation; DCS) have been increasingly used to produce analgesia in patients with chronic pain. This therapy emerged from the gate theory of Melzack and Wall [21] in which it was postulated that:activity:in Coarse p r i m ~ afferent fibres mainly mediating ~touch would lead to preSynaptic inhibition i n the dors~ horn of the activity in thin afferent fibres, mediating pain. The experimental data behind this theory {e.g. ref. 22) have been shown to be partly wrong (see ref. 28). However, there is evidence t h a t dorsal horn neurones, activated by :uoxious C-fibre input and possibly mediating pain centrally, are inhibited by activation of coarse myelinated nerve fibres [ 15]. Moreover, several authors have reported that a clinically useful analgesia can be produced by high frequency stimulation of peripheral nerves at an intensity evoking activity chiefly in coarse myelinated fibres {Fig. 1A) [18,19,23,29,35]. Few followup studies have been published but it seems that in the hands of others as well as in ours this stimulation method is effective only in a minority of patients with chronic pain [ 18--20, cf. however 27]. To :~nprove the results of peripheral conditioning stimulation for analgesia, we recently developed a new kind of such stimulation [11] where experiences from the Chinese electro-acupuncture were utilized. With electroacupuncture, high intensity electrical pulses are given via the inserted needles, usually at a low frequency of about 1--2/sec (Fig. 1B) [2,17]. Surgical procedures may be performed with electro-acupuncture as the only analgesic measure [6,17] and in healthy volunteers the threshold for experimental tooth pain was found to rise [2,8,16]. Furthermore, stimulation of deep afferents was reported to be vssential for the effect [9], whereas surface electrodes could be substituted for the needles provided that strong muscle contractions were elicited in segmentally related myotomes [4]. When tried clinically, patients with chronic pain generally did not tolerate the stimulation strength necessary to elicit strong muscle twitches near the painful area [ 3]. However, when we substituted a brief train of impulses for the single impulse (Fig, 1C) it was possible to decrease t h e stimulation strength to tolerable levels, maintaining t h e muscle twitches and the induction o f analgesia in patien,~s with chronic pain resistant to conventional high frequency stimulation [ 11,12 ]. A

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337

In the present report we describe the results of a 2 year follow-up of 123 patients with chronic pain treated with either t y p e of peripheral conditioning stimulation. All the patients first tried conventional high frequency stimulation and :if the analgesia was not sufficient, t h e y were instead treated with acupuncture-like low frequency train stimulation. As will be shown, the c o m p i l e d results were then improved as compared to those o f conventional TNS alone. Furthermore, peripheral conditioning stimulation appears to be a valuable tool in the long term treatment of chronic pain. METHODS

The study was performed on those patients consecutively referred during 18 months to the pain treatment group of Lund University Hospital for symptomatic pain treatment. We have excluded 6 patients who died from their pain causing disease within 1 week, 2 patients who needed aetiological therapy and one patient who moved abroad and could not be followed. The age distribution of the remaining 123 patients is shown in Fig. 3A {median age 61 years) and the sex distribution was 78 males and 45 females. Stimulation treatment was given according to a fixed schedule in our open care unit by two of us (M.E. and B.S.). The patient was first subjected to a neurological examination and then conventional bigh frequency stimulation was performed during a long session with several electrode locations. If some analgesia was reported the patient was allowed to try the stimulation at home for 1--2 weeks and to vary the stimulation frequency within the 10-100 Hz range to get the best results. If no analgesia was reported at the first session or was insufficient after the initial trial period, the patient was instead given acupuncture-like stimulation during another long test session, care being taken to produce strong muscle twitches in myotomes segmentally related to the painful area. If after another trial period at home this stimulation did n o t produce analgesia, the patient was excluded from further stimulation treatment and was registered as a failure. If the stimulation treatment did produce useful analgesia, defined as a desire from the patient to continue the treatment, the patient received his own stimulator and was seen with regular intervals for 2 years or until the treatment was terminated. In addition, all patients with no physical signs of somatic disease and negative laboratory tests {diagnostic radiology, electromyography), as well as those who never reported any useful analgesia, were referred to a blind psychiatric evaluation by one of us (S.N.). After 3 months of treatment all the patients still using stimulators filled in questionnaires and scored their pain intensity on a visual analogue scale [ 26 ] before and after stimulation. They were also asked how often they used the equipment, about their previous and present analgesic intake and about possible changes in their social activity after stimulation, The stimulator used {Fig. 2) is a portable constant current unit that delivers monophasic square wave pulses of 0.2 msec duration at maximally 60 mA into a load o f 2500 F$, manufactured according to our specifications

338

Fig. 2. Portable constant current stimulator for conventional and acupuncture-like TNS. Carbon rubber electrodes over median nerve. See text.

(CEFAR Medical Pro,clucts, S-222 27 Lund, Sweden). Both conventional high frequency TNS (10--100 Hz; Fig. 1A) and acupuncture-like low frequency TNS (train duration 70 msec and internal frequency 100 Hz; repetition rate 1--4 Hz; Fig. 1C) can be produced. The stimulation was given via standard carbon rubber electrodes size 14 cm 2 (Fig. 2), coated with conducting gel and placed within or around the painful area or over nerve branches innervating the painful dermatome (conventional TNS) [25] or the corresponding myotome (acupuncture-like TNS). The stimulation intensity was 2.5--3 times the perception threshold in conventional TNS (usually 12--30 mA) and 3--5 times :~he perception threshold in acupuncture-like TNS (usually 15--50 mA; cf. Fig. 1) [11]. The duration of stimulation was initially 3{) rain, 3 times daily and then varied according to individual needs (cf. Results). RESULTS

From the histogram of Fig. 3B it appears that out of the 123 patients given stimulation treatment (hatched bar) 68 patients (55%) continued the treatment after 3 months, 50 patients (41%) continued after 1 year and 38 patients (31%) continued after 2 years. In these numbers are included 6 patients who died between 1 and 3 months after the start of stimulation, 4 patients who died between 3 and 12 months after the start of stimulation

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avd 3 patients who died b e ~ e e n 1 and 2 years of stimulation, all with useful ar :aJgesm ~m rne~r ueams.

gp.nic (Fig. 4C) factors ['24],:O~ya few patients interrupted thel st--ulation treatment b ~ a u s e of difficulties to cope with the technique (Fig, 4B) ordue to t h e devel0Pment of tolerance (Fig. 4E). Ohm,of those w h o discontinued due tol changes i n pain intensity, 6/12 had experienced a spontaneous decrease of thepain since the start of the treatment (Fig. 4D). As concerns Zthe degree of pain relief scored after 3 months on a visual analogue scale, the majority (72%) of patients with useful analgesia indicated more than 50% pain relief (Fig. 3C), whereas only 28% indicated less than 30% relief (Fig. 3D). Interestingly, after 24 months the proportions were approx~ately the same, 79% versus 21%. AetioIo~c~ factors a n d t h e location o f pain influenced the results as can be seen from Table I. Here the patients are grouped according to these variables inrelation to: how many of them that continued the treatment after 3 months, i.e. the patients who never experienced any useful analgesia had discontinued the treatment (Fig. 4). It is evident that neuralgia, especially in the face (group la; atypical and typical trigeminal neuralgia) [cf. 13] but also at other locations {group lb) could often be controlled with . . . . .

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341 TABLE I NUMBER OF PATIENTS STARTING STIMULATION TREATMENT AND CONTINUING A F T E R 3 MONTHS, GROUPED ACCORDING TO CAUSE (AND LOCATION) OF PAIN

( ) = patients using acupuncture-like TNS. See text. Cause (and location) of pain 1. Neuralgia (a) in face (b) in other locations 2. Rhizalgia 3. Dorsaigia 4. Centrally evoked pain 5. Cancer pain (a) in parietal structures (b) in visceral structures 6. Ischaemic pain in extremities 7. Psychogenic pain In total

Stetting treatment

Continuing after :3 months

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123

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peripheral conditioning lstimulation. The latter group consisted of patients with neuralgia due to both trauma, inflammatory and metabolic disorders. ~o rh~~ (2 cervical, 20 lumb~)and dorsalgia could often be relieved (groups 2 and 3). Inthe c~e of pain due to a lesion of the centr~ nervous sys~m~igroUp 4), 5/7 patients With d ~ a g e rostral to the spine] cord and 7/11 with damage to the s p i ~ co.rd and roots experienced useful an~gesia 0fwhich 6 / 7 of the latter ~ d pain at the level of the lesion. Concerning c ~ c e r P ~ i t w ~ i n 4/6 cases possible to relieve considerably the pain of metastas~ ~ the ske!e~n ( ~ o u p 5a) but not as a rule that due to cancer g r o ~ h in v~ceral Structures (group 5b). N~ither was treatment of ischemic

342

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Fig. 5. A: total number of patients continuing treatment for 1 year. B: number of patients on which destructive surgery had been undertaken. C" number of patients w i t h hypaesthesia in and around painful area. Bars according to k , : , y . . . . . . . . .......... ~ .

had a cutaneous hypaesthesia in:and around the painful area whereas this was so only ina mlnority:of cases (9/35) using Conventional TNS (Fig, 5C). How did the st~ulation treatment influence the life o f a patknt:; with chronic pain? In Table II, data from 50 pati~n~ using the, :tzeatment more than 1 year are shown. Among the patients with more than 50% pain relief 16/36 had substantially decreased their intake of analgesics and I8/36 had increased the~ s o c ~ l activity [ cf. 19]. On the other hand, in spite of about as frequent of: :the: st~Ulati~n ::i:epo~ing less

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TABLE II QUESTIONNAIRE DATA FROM 50 PATIENTS ON STIMULATION TREATMENT FOR 1 YEAR .

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36 (9~

144 (6.)

Increased social activity ~