The Efficacy Of Magnesium In Radicular Lower Limb Pain When It Is Added To Local Anesthetics And Steroids In The Transforaminal Epidural Injections. A Comparative Study

INTRODUCTION:

One of the common presentation of low back pain and lower extremities pain is lumbar radicular pain which may be caused by a herniated intervertebral disc exerting a pressure on nerve roots, resulting in pain, functional disability, opioid use for pain relief and consuming health resources (1,2). Radicular pain has a typical shocking, lancinating, or electric character traveling into the lower limb along a narrow band. In approximately 90% of cases, radiculopathy is mainly due to a prolapsed disc causing nerve root impingement (3). Different modalities of treatments are used in managing chronic low back pain and radiculopathy. Most of the patients will respond well to conservative management. But after the failure of this conservative treatment, either surgical or nonsurgical modalities such as epidural injections are going to be considered in the treatment of lumbar radiculopathy (4). Transforaminal epidural injection (TFEI) is a known approach for treatment of spinal nerve root pathology. A transforaminal epidural directs medications at the nerve root as it leaves the spinal cord at the ventrolateral aspect of the epidural space whereas a conventional (interlaminar) epidural results in a small amount of medication over a wide area at the posterior epidural space (5). A transforaminal epidural gives us the opportunity to allocate the medications where they are required (6). Transforaminal epidural injections under fluoroscopic guidance have emerged as the preferred approach to the epidural space (7). Many drugs have been proven to be effective in managing low back pain when they are injected in the epidural space by transforaminal approach such as local anesthetics, steroids and adjuvants (7). Magnesium is a physiological blocker of the NMDA receptors (8) because it blocks NMDA channels in a voltage-dependent manner, and such NMDA antagonist effect can inhibit the induction of central sensitization from peripheral nociceptive stimulation (9,10). Magnesium may suppress neuropathic pain (11), enhance morphine analgesia, attenuate morphine tolerance (12), and improve fentanyl analgesia when magnesium is given intrathecally (13). Magnesium deficiency produces hyperalgesia (14) and has been related to cause some acute medical and surgical conditions in which pain or stress is present (15). Magnesium is proved to be injected safely within the nervous tissue in animals (16) and in 2002 Asokumar and his colleagues proved that magnesium is safely injected Intrathecal in human (17). Because of the results of a previous study that indicates that intrathecal administration of sulfate sault in magnesium has a risk of neurotoxicity (18), investigators preferred to use preservative free magnesium in our study. The aim of this study was to evaluate the efficacy of magnesium sulphate as an anti-neuropathic drug in relieving unilateral lower limb radicular pain due to disc prolapse when it was injected with lidocaine and steroids in the anterior epidural space using the transforaminal epidural approach. Our primary outcome was to assess the improvement of pain score post-injection, while, the secondary outcome was to evaluate the improvement of the functional ability and the satisfaction level of the patients after the procedure.

Patients and Methods:

Firstly, The study IS approved by the local ethics committee (Fayoum Faculty of Medicine Research Ethics Committee R139 ). This prospective, controlled, randomized, double-blinded study is going to be carried out in the pain management department of Fayoum University Hospital. Written consents are going to be taken from all patients. The randomization is going to be performed via sealed opaque envelopes. All procedures are going to be performed by one investigator who is blind to the injected drugs used in this study. Inclusion criteria are patients of both gender, aged from 20 up to 70 years old, American Society of Anesthesiologists (ASA) physical status grade I and II (19), admitted for pain management of their unilateral lower limb radicular pain due to lumbo-sacral disc prolapse confirmed by lumbo-sacral magnetic resonance imaging ( MRI) after failure of conservative treatments in the form of drug therapy and physiotherapy to control the pain for 6 weeks. Exclusion criteria are patients with axial back pain without leg radiation, patients with motor neurological deficits, previous spine surgeries, allergy to the study drugs used, uncontrolled diabetes mellitus or hypertension, local or systemic infection, pregnancy, and patients with any other neurological deficits as cauda equina. This study is going to be conducted on 100 patients. Patients are going to be divided according to the injected drugs into two equal groups (50 patients each):

1. Group (C): where all patients will receive through the transforaminal epidural approach 2 ml of bupivacaine (0.5%), 1ml of methylprednisolone (40 mg) and 1 ml of normal saline (0.9 %) with a total volume of 4 ml.
2. Group (M): where all patients will receive through the transforaminal epidural approach 2 ml of bupivacaine (0.5%), 1ml of methylprednisolone (40 mg) and 1 ml of preservative free magnesium (200 mg) with a total volume of 4 ml. Methylprednisolone which is used in this study is going to be supplied from E.I.P.I.C.O pharmaceuticals -Egypt under license of UPJOHN s.a Puurs-Belgium (Depo-Medrol). Preservative free magnesium which is used in the study is prepared in McGuff Pharmaceuticals, Inc. Laboratories and supplied in 50 ml vials containing magnesium (200 mg/ml).