Dr Gail Gillespie
Specialist Registrar in Anaesthesia & Pain Management, South Glasgow Hospitals NHS Trust
Dr Pete MacKenzie
Consultant Anaesthetist & Specialist in Pain Management, South Glasgow Hospitals NHS Trust
SMJ 2004 49(3): 79-81
Keywords:
Epiduroscopy, spinal endoscopy, epidural fibrosis, adhesiolysis, chronic low
back pain, radiculopathy,
Introduction
Spinal
endoscopy, or “epiduroscopy”, is the examination of the epidural space by a
minimally invasive technique that allows the diagnosis and treatment of chronic
back pain and radiculopathy.
Myeloscopy,
the direct examination of the spinal intrathecal canal and its contents, was
first described by Michael Burman in 1931.
Myeloscopy was initially used in cadavers, but by 1937 it was being used
in vivo by Dr J Lawrence Pool of New York to diagnose lesions affecting the
cauda equina and lower end of spinal cord. (1) Myeloscopy however could not
allow visualization of the nerve roots or soft tissues in the epidural canal.
There
was little work carried out in this field until 1969, when Ooi et al. became the
first to take clear colour endoscopic pictures of the spinal canal via a newly
designed fibreoptic system. (2)By 1985, Blomberg was using epiduroscopy to study
the lumbar epidural space at autopsy. (3) In 1989, he carried out the first
percutaneous epiduroscopy in living subjects via a lumbar approach using a rigid
arthroscope. (4)Fibreoptics remained poor, however, and the procedure was
further complicated by difficulties visualizing a potential space often
obliterated by bleeding. In the early 1990s, Heavner, Shimoji and Schutze each
described the use of small diameter flexible fibreoptic endoscopes for
visualization of the epidural space. (5,6,7)
The Myelotec flexible fibreoptic endoscope combines both the image fibre bundle and illumination fibre bundle in a 0.9mm flexible fibreoptic endoscope.( Fig 1.)
Despite
these advances, the acute angle of entry of the endoscope into the lumbar
epidural space meant that
manoeuvring the
endoscope in this space remained difficult. A straight
angle of entry via sacral hiatus was found to facilitate steering of endoscope in all planes within the
epidural space. (8) By 1996
the advent of a video-guided catheter system (Myelotec®) allowed an easily
steerable system through which the epidural endoscopy system could be fed. Thus,
improved manoeuvrability, coupled with saline distension of the epidural canal,
gave better visualization allowing real-time colour images of the epidural canal.
Fig
2. Video Guided Catheter (image courtesy of Visionary Biomedical, Inc.).
The therapeutic potential of epiduroscopy and adhesiolysis, a minimally
invasive but potentially useful treatment modality in the management of
refractory radiculopathy, emerged during the 1990s.
(8)
This review highlights the pathophysiology of radiculopathy and Failed Back
Surgery Syndrome and discusses the therapeutic use of epidural steroids. It also
covers various aspects of epiduroscopy including indications, clinical
technique, complications and clinical effectiveness base on current evidence.
Radiculopathy
Most
patients suffering an episode of acute severe back pain with radicular symptoms
recover within a month. A third of
patients, however, still have pain, decreased activity and a decreased capacity
for work one year later. (9) While epidural adhesions most commonly result
following surgical intervention of the spine, they can also appear in patients
who have not previously had surgery. This is confirmed by epiduroscopy of
patients with chronic radiculopathy, who have not previously undergone surgery,
displaying extensive epidural fibrosis and adhesions. Possible causes of such
fibrosis include leakage of disc material from the nucleus pulposus into the
epidural space or the inflammatory response following an anular tear. There is
evidence from animal studies that cytokines present within the nucleus pulposus
can cause a painful neuropathy if applied to intact nerves. (10) Leakage of
these antigenic disc contents continues to stimulate the inflammatory process in
the local perineural region, thus sustaining the chemical radiculitis. Radicular
pain may then become persistent following resolution of disc herniation, due to
compression or traction caused by epidural adhesions and fibrosis. Such scarring
around nerve roots may also cause a decrease in the nerve root microcirculation,
resulting in ischaemia and subsequent abnormalities in nerve conduction. Such
radicular pathology may contribute to the generation and maintenance of this
neuropathic pain. Current diagnostic techniques such as CT, MRI, myelography,
and electromyography can fail to highlight this soft tissue pathology within the
epidural canal.
Failed
Back Surgery Syndrome
Although
surgical discectomy for disc herniation, produces better short term pain relief
than conservative therapy, there is no convincing evidence for the long term (10
years) advantage of surgery.(11) Between
40% and 80% of patients undergoing back surgery continue to experience
persistent pain, a condition called Failed Back Surgery Syndrome (FBSS). The
symptoms of FBSS are of persistent or recurring low back pain and / or leg pain
after one or more spinal operations. The precise cause of the pain can be
difficult to determine due to the complex interaction of biological and
psychosocial factors. Possible organic causes of FBSS include epidural
fibrosis, arachnoiditis, mechanical factors, pressure induced changes in the
nerve root, structural changes in the vertebral column, and lumbar degenerative
disease. With a second surgical intervention for fibrosis, there is a 65-70%
failure rate, with 15-20% of the patients reporting worsening of symptoms. (12)
Thus, repeated surgery tends to yield poorer results.
Use
of Epidural Steroids in the management of Radiculopathy
Epidural corticosteroids are commonly used in the treatment of low back
pain with radiculopathy, although steroids are not currently licensed for
epidural use in UK. The mode of action of steroids in this context is unclear.
Suggested mechanisms relate to their anti-inflammatory properties and their
inhibitory effect on C fibre conduction.
What
is the efficacy of epidural steroids for treatment of radiculopathy? A
meta-analysis by Watts and Silagy (13) showed a statistically significant
benefit of epidural steroid as compared to control. Combined results from ten
trials with short term outcomes showed that epidural administration of
corticosteroids is effective in the management of sciatica with a NNT of 7.3 for
>75% pain relief in the short-term (1-60days). Six trials had long-term
relief data (12 weeks – 1 year) and an overall NNT of 13 for 50% relief in the
long term. (14) The addition of clonidine and hyaluronidase to the
corticosteroid has also been described. (15,16,17)
Blind
epidural injection of a therapeutic substance can, in some patients, fail to
flow towards a symptomatic root due to obstruction by epidural fibrosis. Such
patients may, therefore, benefit more from epidural injection if flow of
injectate towards the symptomatic root is facilitated following endoscopic
division of epidural adhesions.
Epiduroscopy
- Method:
Epiduroscopy
is carried out under local anaesthesia with the patient awake, thus avoiding
potential unrecognized pressure effects in the epidural canal.
Light intravenous sedation and analgesia may be required to ensure full
patient cooperation while maintaining verbal contact. The patient is positioned
prone with a pillow under his/her hips. The procedure is carried out under
aseptic conditions with antibiotic prophylaxis and requires the use of an
imagine intensifier. Sacrococcygeal ligament puncture is made with a 17g Tuohy
needle and followed by a caudal epidurogram to confirm needle placement. A
Seldinger technique is then used to place an introducer sheath in the sacral
epidural canal. A 0.9mm fibreoptic scope is placed with its tip and the end of a
steerable video guided catheter.
The
VGC and endoscope are then advanced via the introducer into epidural space. Slow
irrigation with saline allows visualization of epidural space by gentle
distension. Adhesiolysis can be carried out under direct vision by blunt
dissection of the adhesions using the tip of the VGC. Blunt dissection coupled
with hydrostatic distension of the epidural space thus creates a pocket through
which injected drug can access symptomatic nerve roots.
Advantages
of epiduroscopy:
(1)
Confirmation of diagnosis: specifically detection of nerve root pathology,
fibrosis and adhesions
(
fig 5.)
(2)
Demonstration of lesions that may not be visible on MRI scan (18)
(3)
Minimally invasive method of treating radicular pathology and creating a track
for injection of therapeutic solutions towards affected nerve roots.
(4)
Allows targeted drug therapy including steroid, local anaesthetic, hyaluronidase,
saline and clonidine.
Disadvantages
of epiduroscopy:
(1)There
is risk of perforation of the dural sac and resultant post-dural puncture
headache.
(2)The
epidural space is only a potential space that requires distension for
visualization. This demands an infusion of saline, which can result in
complications if volume infused is excessive or under pressure. Cervicalgia,
headache and paraesthesia are described side effects. These can be minimized by
reducing volume and pressure of infused saline.
(3)Transient
blindness due to retinal haemorrhage has been reported in 10 patients undergoing
epidural steroid injection. This has been associated with high cranial CSF
pressures generated by bulk displacement of spinal CSF during rapid epidural
injection. One case of acute visual loss associated with
retinal hemorrhages following epiduroscopy
has been reported. This resolved completely within 6
months. (19) This complication may be decreased by
decreasing the rate and volume of epidural injection, thus minimizing raises in
CSF pressure. Caution should be exercised before carrying out epiduroscopy in
patients with compromised retinal circulation, and the risks should be
discussed.
(4) General tonic-clonic and lower limb spasms have been described during epiduroscopy which were attributed to medulla-radicular irritation. In all cases, patients were anaesthetized and very large volumes of irrigation fluid were used (300-1200ml). No long-term sequelae persisted. (20) In view of these reports, it is now considered safe practice to avoid general anesthesia and limit the volume of irrigated solution to around 150ml.
(5)
The diagnostic value of epiduroscopy may be limited during the learning curve
and in cases where visualization is obscured by epidural fat and blood vessels.
Clinical
Effectiveness:
There
is little outcome data on patients undergoing therapeutic epiduroscopy with few
rigorous trials with sufficient numbers. Early
results from recent prospective studies by Richardson et al showed significant
reductions in pain scores and disability at 6 months to 1 year. The numbers in
this study were small, however, and it may have been underpowered for outcome
analysis but results were encouraging. (15,17) A recent randomized double-blind
trial by Manchkanti et al.(21) looked at epiduroscopy with adhesiolysis plus
targeted local and steroid injection compared with a control group who had
epiduroscopy to the sacral level and injection of local with steroid but without
adhesiolysis. Significant improvement with regard to pain relief and improved
function in the adhesiolysis group was maintained at 1, 3 and 6 months compared
to baseline and control group, with 57% patients showing significant
improvement. Although numbers in the study were small, this study described no
major adverse effects with this technique and medium term benefits are
encouraging. It is acknowledged that further follow up studies and larger
randsomised controlled trials are required to evaluate the longer term benefits
of this promising technique. (21)
Conclusions
Epiduroscopy
with division of adhesions and targeted epidural injection is a promising and
relatively safe minimally-invasive intervention for the management of painful
radiculopathy.
This
technique may have therapeutic advantages over blind epidural steroid injection
and provides a less invasive alternative to disc surgery. Furthermore, direct
visualization of epidural pathology provides diagnostic advantages over MRI.
(17) Further large controlled studies are required to assess the therapeutic
role and cost effectiveness of epiduroscopy.
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(2)Ooi
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(15)Geurts
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Acknowledgements
Ian
Lomas, Myelotec/Promed Ltd for permission to print images