Internal Disc Disruption (IDD) and Intervertebral Disc Herniation (IDH) are the major causes of low-back pain and sciatica.
Internal Disc Disruption leads to the “discogenic pain”, characterized by diffuse, dull ache or deep-seated, burning, lancinating pain in the low back with not uncommon irradiation into the leg as referred pain without nerve root entrapment. The pathophysiological mechanism consists of annulus tears, in-growth of granulation tissue and of nociceptive nerve endings, irritation by chemical materials inside the disc or from the epidural area and mechanical stimulation associated with lumbar movement on the sinuvertebral nerve ending distributed in the outer one-third of the annulus and posterior longitudinal ligament. About 39% of all patients with chronic low back pain have IDD. At present the diagnosis of discogenic pain is fundamentally based on the typical symptoms, images on MRI (“black disc” and middle annulus fibrosus bulge) and results of discography that became the main diagnostic criteria. Most patients suffering from discogenic pain show positive in discography and express the similar or exact pain as usual, including quality, location and severity, but sometimes there are some exceptions. Current therapeutic approaches include pharmacologic pain control, minimal invasive interventional procedures on the disc and lumbar interbody fusion [11
] (Figure 3).
Herniation of lumbar intervertebral disc is the most common cause of low back pain with classical predominantly irradiation along the nerve route course. The process of annular ruptures, disc herniation
and nerve root compression can result in a complex picture of symptoms and signs that represents a combination of somatic pain from the outer annulus and posterior longitudinal ligaments and neuropathic radicular pain from nerve root compression together with chemical reaction. In this study, we investigated the therapeutic outcome of percutaneous intradiscal injections of radiopaque gelified ethanol (Discogel) (group 1) vs intraforaminal and intradiscal injections of a steroid and an anesthetic (group 2) in 144 patients with lumbar disc herniation. In group 1, over ninety percent of patients showed excellent or good result that substantially maintained unchanged during follow-up. These percentages were significantly higher than those reported in group 2. Rihn et al., in a recent study, showed that obesity realized less clinical benefit from both operative and non-operative treatment in 336 obese patients with lumbar disc herniation. Nevertheless, in our patients after adjustment for BMI the benefit of Discogel treatment remained strongly significant [13
] (Figure 4).
Surgery is considered the treatment of choice for extruded, migrated hand free fragment herniated disc and absolute indication in presence of hyperalgic sciatalgia, sphincteral deficit and progressive neurological deficits.
The possible suboptimal results of surgery and its complications lead to the development of minimally invasive ablative percutaneous techniques that could be offered as alternative to surgical treatment [14
]. These techniques are image-guided procedures based on the puncture of the annulus with a trocar: through this trocar chemical, thermal or mechanical ablative device may be placed inside the nucleus pulposus [5
]. These procedures seem to have established a new concept of “alternative intermediate therapy” [16
] in treatment of lumbar herniation. The most relevant agent used in the past for chemical percutaneous technique was Chymopapain. The effectiveness of chemonucleolysis with this enzyme has been widely documented [6
]. Nevertheless possible side effects and complications as major pain after treatment, systemic allergic reactions, chemical discitis and transverse myelitis [18
], leaded to the necessity of new chemonucleolytic substance. However 96%, pure ethanol was used with good results [4
]: alcohol produces a molecular scission of proteoglycans and glucosaminoglycans of the nucleus pulposus and consequently a chemical decompression of the disc [19
]. Pure ethanol is difficult to handle due to its ready diffusion into the tissues. It indiscriminately attacks annulus, cartilage, vessel, root and dura: discography must be performed before inject ethanol to determine degree of disc degeneration and leakage of contrast into the epidural space
, vascular and intraosseus areas; furthermore it cannot be visualized on fluoroscopy
“Discogel” is a viscous solution consisting in ethanol mixed with ethyl cellulose and tungsten (radiopaque gelified ethanol) that causes a local necrosis of nucleous pulposus and dehydration of the turgescent and protruding disc; thus resulting in retraction of intervertebral disc herniation.
The use of the ethyl cellulose increases the viscosity limiting the ethanol diffusion in the disc and performs a simultaneous deposition of a part of the gel which precipitates making a kind of soft intradiscal “prosthesis”. The tungsten makes the product radiopaque and the amount of gel injected can be monitored with fluoroscopy. The distribution of the product in the axial plane therefore became apparent on CT examination and of major interest is the visualization of the fissures of the annulus and the migration of the product into the symptomatic hernia. The viscosity of gelified ethyl alcohol depends on temperature. Administration of the product warmed up above room temperature should be avoided because the gel becomes more liquid and is below optimum viscosity. In an experimental study Guarnieri [14
] showed that “Discogel” produces no morpho-structural changes in the nuclear tissue and annulus and in contact with nervous structure.
The pathogenesis of low back and radicular pain in presence of a herniated disc is multifactorial: it is characterized by mechanical factors, direct or indirect, and by associated inflammatory factors, cell-mediated inflammatory reaction and bio-humoral immunological response. Direct mechanical factors are direct compression of herniated disk on the spinal ganglion and mechanical deformation of posterior longitudinal ligament and annulus with nociceptor stimulation of the recurrent nerve of Lutschka. Indirect mechanical factors are ischemia due to compression on afferent arterioles and nerve bundle microcirculation with anoxic demyelination and venous stasis. Neural inflammation is also important: it is due to autoimmune cell-mediated response to proteoglycans of the herniated fragment and to bio-humoral immunological response due to prostaglandin (PGE2) and leucotrieni produced by phospholipase A2 from arachidonic acid, matrix metalloproteinase (MMP-1-2-2-9), IL-1, IL-6, TNF-alfa. Low back and radicular pain improvement after the intradiscal “Discogel” injection may be due to the dehydration
of nucleus pulposus with reduction of intradiscal pressure and retraction of the disc herniation. According with Theron [3
] we believe that the most important intradiscal therapeutic reaction is not the immediate reduction of the hernia volume but the decrease of the intradiscal pressure allowing a partial decompressive shift of the herniated nucleus: in our study this is well evidenced by the discordance between the rapid improvement of clinical symptoms and the radiologic image of unchanged volume of disc herniation on CT scan at 1 and 3 months after “Discogel” injection. It is also conceivable a direct effect of ethanol on the disc pain receptors by turning out the nervous endings. Coppes [20
] and Freemont [19
] demonstrated the presence of nerve fibers into the inner layers of the annulus fibrosus and in the nucleus pulposus in degenerative painful discs and not in normal discs.
] reported a success rate of 91.4% in a group of 221 patients with lumbar disc hernias and a complication rate <0.5%, while Stagni [21
] a therapeutic success in 24 out of 32 treated patients (75%) without complications. Complications described for the use of Discogel are systemic allergic reactions to the substance, discitis
and neurologic injury. In our series we obtained pain improvement > 50% in 90.3% of cases and only few transitory complications: 1 sensory-motor deficit and 3 appearance of neuropathic pain.
Our study has some limitations: first of all this was an observational open-label study; another limitations is the small sample of patients. Still the evaluation was complete and accurate in all patients and performed by a physician experienced in this issue.