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Lumbar Spinal Stenosis | Nerve Root Impingement

Lumbar spinal stenosis is a narrowing of the central spinal canal in the lower back, specifically at the lumbar levels. Nerve root impingement is a narrowing and subsequent contact of the exiting nerve root, usually at the lateral recess at a specific lumbar level. 

Lumbar Spinal stenosis is a common cause of axial and leg symptoms in patients over the age of 65. Lumbar Spinal Stenosis: Pathophysiology, Biomechanics, and Innovations in Diagnosis and Management – PubMed it typically manifest through age-related changes in the spine, including discopathy (dehydration of the disks +/- disc bulges and extrusions). ligamentum flavum hypertrophy and facet joint arthropathy (wear and tear of the facet joint of the lumbar spine) Lumbar Spinal Stenosis – StatPearls – NCBI Bookshelf. These changes result in narrowing of the central canal, most commonly at the L4/L5 level. Spinal Stenosis and Neurogenic Claudication – StatPearls – NCBI Bookshelf with impingement of the thecal sac and spinal segments. This condition, though significantly less common, can also affect the young patient and is usually due to an specific injury resulting in an acute central disc prolapse/herniation with contact of the central canal structures. Lumbar canal stenosis in “young” – How does it differ from that in “old” – An analysis of 116 surgically treated cases – PMC.

Nerve root impingement is a common cause of unilateral leg symptoms which affect the young and old. It typically manifests through both age-related changes and an acute disc prolapse/herniation, with the compression site usually at the lateral recess or neural foreman (the opening between the vertebras) most commonly at the L4/L5 and L5/S1 levels  Lumbosacral Radiculopathy – StatPearls – NCBI Bookshelf.

What are the signs and symptoms?

For the vast majority of patients, lower back pain with or without leg symptoms will resolve within 12 weeks. For patients with persisting symptoms, leg pain significantly worse than back pain, motor weakness or acute bowel and bladder symptoms, an MRI will be indicated either routinely, urgently or immediately in an A and E service depending on the specific set of symptoms.

Spinal stenosis radiographically is common in the asymptomatic population, with up to 80 % of patients above the age of 45 having evidence of the disease. Lumbar Spinal Stenosis – StatPearls – NCBI Bookshelf. For symptomatic cases patients typically complain of leg pain (unilateral or bilateral) +/- lower back pain. Symptoms are typically worse with periods of ambulation or standing and eased with sitting or bending forwards. In severe cases there may be weakness in the legs, constant anaesthesia or paraesthesia in the lower limbs and, in rare cases, acute changes in bowel and/or bladder function as the cauda equina nerve roots (nerves supplying sensation of the saddle region and action of the bowel and bladder) become compromised.

Patients with nerve root impingement typically complain of unremitting unilateral leg symptoms +/- lower back pain. In severe cases there can be associated weakness of the specific nerve root, the most common being acute foot drop due to a deficit of the L4 nerve root. Rarely can cauda equina signs and symptoms also be present, which will require immediate medical input/imaging and neurosurgical work-up. Acute and severe leg symptoms in a young/middle-aged patient require careful assessment and safety netting, as these patients are at a significantly higher risk of developing cauda equina syndrome when compared to the chronic, elderly, stenotic patient. Cauda Equina and Conus Medullaris Syndromes – StatPearls – NCBI Bookshelf.

How is it diagnosed?

The diagnosis will be made from a combination of your clinical history, examination findings and, in necessary cases, an MRI scan. Imaging requests can be categorised into routine, urgent or emergency cases depending on the patients’ symptoms and neurological examination. 

  • For patients with leg pain that are neurologically intact and have no cauda equina signs and symptoms, all that may be indicated in this cohort of patients is reassurance, appropriate safety netting and time for things to settle. Routine imaging may be indicated if there is progression of leg symptoms or if things have failed to respond to conservative management.
  • For patients with severe leg symptoms, with evidence of acute motor deficit on neurological examination, MRI will typically be indicated at presentation (urgently) to confirm the extent and cause where surgical input is likely to be considered.
  • For patients with severe leg symptoms, unilateral or bilateral, with associated motor weakness and/or cauda equina symptoms (less than 2 weeks old), these patients will be directed to AE services for immediate/emergency imaging to exclude cauda equina syndrome. Delayed diagnosis of this condition leads to irreversible neurological damage of the sacral nerve roots with often permanent urinary and faecal incontinence. Cauda Equina and Conus Medullaris Syndromes – StatPearls – NCBI Bookshelf. Luckily the condition is rare with an estimated prevalence of 1 in 100000 patients. Demographics of Cauda Equina Syndrome: A Population-Based Incidence Study – PubMed

MRI is the gold standard for assessing the cause of neurological compromise with aetiologies including, most commonly, mechanical (e.g. disc herniations, spondylosis, spondylolisthesis) and, in rare cases, benign space-occupying lesions (cysts, vascular malformations and nerve sheath tumours), malignancies (primary and secondary), infections and traumatic causes. The Role of MRI in Evaluating Spinal Cord Injuries: Diagnostic Accuracy, Prognostic Value, and Clinical Decision-Making – PMC

How is it treated?

Treatment options are divided into conservative and surgical.

Conservative options: (Where appropriate and red flags have been excluded)

  • Period of relative rest. For acute episodes of lower back pain +/- leg symptoms (without red flag symptoms), the vast majority will self-resolve within 12 weeks without any medical input. Lumbosacral Radiculopathy – StatPearls – NCBI Bookshelf
  • Medications can be helpful at reducing radicular leg symptoms while the nature of the disease runs its course. Medications may include gabapentinoids (gabapentin and pregabalin), Tricyclic antidepressants (amitriptyline) and SNRIs (duloxetine). The neuropathic pain: An overview of the current treatment and future therapeutic approaches – PMC these have been shown to have a better effect than opioid-based medications.
  • Physiotherapy and exercise. This is an important aspect of any lower back complaint to reduce the risk of chronic symptoms, improving spinal capacity, resilience and tolerance. The best exercises are the ones the patient will be compliant with. Evidence does not support one specific rehab/exercise programme over another. Exercise intervention for patients with chronic low back pain: a systematic review and network meta-analysis – PubMed
  • For refractory cases. A caudal epidural can be helpful in carefully selected patients (No motor weakness, no red flags, L5/S1 or L4/L5 stenosis on recent MRI, leg pain worse than back pain, with no improvement at 4 weeks from initial onset). Through visualisation of the sacral hiatus, cornua and sacrococcygeal ligament, medication (steroid, +/- small amount of local anaesthetic and saline) can be injected into the epidural space under ultrasound guidance to bath the compressed spinal nerve roots, reducing local inflammatory effects and subsequent leg pain. It is a safe and effective treatment which can provide long-term resolution of symptoms in certain patients. Ultrasound-guided caudal epidural injection to treat symptoms of lumbar spinal stenosis: a retrospective study – PubMed There are other approaches, interlaminar and transforaminal, along with specific nerve root injections that can also be considered but are not utilised in our clinics.

Surgical intervention:

For patients with persisting leg symptoms, evidence of motor deficit or red flag symptoms (bowel and bladder symptoms) with clear MRI correlation surgical decompression is indicated. 

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