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Differential diagnosis / clinical reasoning: Back pain

Updated: Mar 7, 2022

 

Classification Aims:

Mechanical: Pain from the vertebral column such as from the facet or sacroiliac joints, vertebral bodies, muscles, ligaments, or discs


Neuropathic: Injury or lesion of the somatosensory system. This occurs in 40-60% of LBP


Both: e.g. Hypertrophy of the facet joints can cause mechanical LBP but also compress an exiting nerve root - and degenerative discs (common cause of mechanical back pain) can also cause nerve root impingement

 

Diagnostic approach:


Types:

Nociceptive, neuropathic, or sensitisation

Somatic referred, Radicular, Radiculopathy


Radicular pain: Ectopic discharges from dorsal root or ganglion. Usually from spinal compressive factors. L4/L5/S1 can be difficult to discern from each other


Radiculopathy: Conduction block of spinal nerve and its roots. For example, decreased sensory or motor function (can occur without pain)

 

Pathophysiology of pain:

Mechanical/Nociceptive: Activation of nociceptors from injury to muscles, soft tissues, bones, joints or skin


Nociceptive pain is attributable to peripheral receptive terminals in reaction to mechanical, chemical, or thermal stimuli.2 Patients experience the following:


Pain localized to the area of injury/dysfunction, clear proportionate mechanical/anatomical nature to aggravating and easing factors, usually intermittent and sharp with movement and mechanical provocation, may be a more constant dull ache or throb at rest, and the absence of pain in association with other dysesthesias, night pain/disturbed sleep, antalgic postures/movement patterns, and pain variously described as burning, shooting, sharp, or electric-shock-like

The second type, peripheral neuropathic pain, indicates involvement or entrapment in the peripheral nervous system from the dorsal root ganglion or peripheral mononeuropathy stemming from trauma, swelling, or compression.5 This is described as “pain referral in a dermatomal or cutaneous distribution, history of nerve injury, pain provocation with mechanical movement testing that move/load/compress neural tissue.”3


The third type, central sensitization, is a complex type of hypersensitivity of the central nervous system that amplifies the pain experience. Widespread pain, or pain enduring beyond expected healing times, and tactile allodynia, hyperalgesia, behavioral dysfunction, and altered pain perceptions have been suggested to be a part of this category.4 There remain difficulties in diagnosis among this group due to the breadth of potential aberrations within this cluster, but according to Smart et al., predictive rules include the following:


Disproportionate, non-mechanical, unpredictable pattern of pain provocation in response to multiple/non-specific/aggravating/easing factors, pain disproportionate to the nature and extent of injury or pathology, strong association with maladaptive psychosocial factors, and diffuse/non-anatomic areas of pain/tenderness on palpation.4

Neuropathic: Injury directly to the tissues of the nervous system such as peripheral nerves, nerve roots, or spinal cord --> Myelopathy (Myelopathy is an injury to the spinal cord caused by severe compression that may be a result of spinal stenosis, disc degeneration, disc herniation, autoimmune disorders or other trauma.)


So how do you work out the difference between mechanical and neuropathic?

First - Neuropathic pain directly affects nervous tissue thereby bypassing the stage of transduction

Second, injury to a major nerve is more likely to lead to chronic pain than injury to a non nervous structure

 

History taking features:


How and when the pain began

Pain pattern, intensity, duration, location, exacerbating and relieving factors

Associated symptoms such as weakness, numbness, or paraesthesiaes

Red flag symptoms are critical

(Red flag” indicators include history of fever/night sweats, trauma, recent surgery, illicit drug use, weight loss, prior history of cancer, occupational exposure, bowel or bladder incontinence and neurological signs/symptoms.)

Yellow flags should also be asked (psych, legal, social etc)


Neuropathic pain history features:

Neuropathic pain is usually characterized by being spontaneous, burning, shooting, and lancinating. It can be associated with paresthesia, frequently described as “pins and needles.” The patients could describe other abnormal sensations such as hyperalgesia, allodynia, hyperpathia, and dysesthesia.


 

Myofascial pain

80% of LBP has no clear etiology - likely muscles and soft tissues

Spasms and tender points are common on exam

Tight spots that when pushed on reproduce the patients pain can be source of peripheral/central sensitisation

 

Facet arthropathy

10-15% of mechanical back pain - increasing with age

Between 30-60% for neck pain, ~45% for thoracic pain

Significant overlap in referral patterns of pain - e.g. between L4/L5 and L5/S1 facet joint pain and different structures

Paraspinal tenderness may be the only reliable finding consistent with facet-mediated pain

Facet loading examinations does not correlate well with diagnosis

Best diagnosis is a MBB

Imaging not overly helpful - but normal imaging means it is a less likely source of pain

 

Sacroiliac joint pain (Murakami, 2018)

15-25% of mechanical back pain - young adults and elderly

Intra (older person) or extra (younger person) articular pathology

Pain is at or around the PSIS, groin pain, or pain at or around the ischial tuberosity are characteristic of SIJ pain


One finger test is useful for identifying pain areas

85% of patients with pain at or around the PSIS with one finger have SIJ disorders


Periarticular injection is easier, and successful in 80% of cases. They suggest performing this first and only if ineffective, later performing an intra-articular injection



Combination of three tests (Patrick's and Gaenslen's tests) have >75% sens/spec

Best diagnostic test is a low volume anaesthetic injection



Differentials:

Entrapment of superior cluneal nerve

- Usually tender over the iliac crest 7-8cm laterally from spinous process of the lumbar spine

- Pain often spreads into the gluteal region and sometimes the lower leg

- Pain develops when standing from a sitting position, rotating, or by bending the lumbar spine laterally


Iliolumbar ligament syndrome

- It comes form the L5 transverse process and attaches to the iliac crest

- To diagnose there is tenderness near the tip of the L5 transverse process


Sacrotuberous ligament syndrome


Piriformis syndrome

- Causes sciatic-type symptoms

- Tenderness is present on the piriformis muscle or on an entrapment site of the nerve


Entrapment neuropathy of the Superior Gluteal Nerve

- Can be entrapped in the superior foramen of the piriformis muscle

- Tenderness is usually at an entrapment site of the nerve

- Release around teh superior gluteal nerve by injecting physiologic saline can help

 

Internal disc disruption (Discogenic pain)

Accounts for between 20 and 45% of cases of mechanical LBP and more common in younger and middle aged adults


Pain is midline in the low back and worsened with sitting or bending


Pain may radiate into the legs in a non-dermatomal pattern


More midline and less paraspinal tenderness compared with facet- or sacroiliac mediated pain


Diagnosis is from symptoms, degenerative disc changes on imaging, and lack of response to facet and/or sacroiliac joint injections


Provocative discography is the 'gold standard' but has a high false-positive rate in some patients (those with somatisation etc).

30% of patients with chronic neck pain have a history of trauma. 20% of these have IDD alone and another 40% have IDD and facet pathology

Physical exam may be nonspecific

MRI may show loss of disc height, signal intensity, and disc bulging, but is inherently non-specific

Discography carries possible risks of increased risk of future rupture so now rarely performed

 

Herniated Disc

Common in younger people (35-50 yo).

Often intermittent radiation of neuropathic pain in a unilateral dermatomal distribution with leg pain often more significant than back pain

Exam may show sensory changes, motor weakness, or abnormal deep tendon reflexes - all involving the impacted nerve root

A positive SLR is 80% sensitive for L5 or S1 nerve root involvement

Positive crossed straight leg raise test is highly specific for lumbar radiculopathy but low sensitivity

Electrodiagnostic tests can be helpful in challenging cases and is very specific for lumbar radiculopathy

MRI is not usually required

Posterolateral herniation can cause symptoms in the subjacent reversing nerve root (L4/5 affecting L5 nerve root)


Neck disc herniation usually has acute onset of limb pain rather than the slow symptom onset of degenerative changes

Pain is often dermatomal and exacerbated by factors that increase subarachnoid pressure (coughing/sneezing etc)

Spurlings can be done but only has a sensitivity of 50%

Hoffman's sign should be assessed for myelopathy

MRI is the best imaging for cervical radiculopathy but it has low specificity

 

Spinal Stenosis


This is a clinical and radiological diagnosis

More common in people >60 yo

Narrowing of the spinal canal results in unilateral or bilateral neuropathic leg symptoms

Often patients have neurogenic claudication - calf or foot pain that improves with forward bending (shopping cart sign) or rest

Causes include disc bulges, ligamentum flavour hypertrophy, facet hypertrophy, osteophyte formation, and spondylolisthesis (all seen on MRI)

Electrodiagnostic studies may help distinguish spinal stenosis from radiculopathy or other causes of leg pain such as plexopathy (Plexopathy is a disorder of the network of nerves in the brachial or lumbosacral plexus), peripheral neuropathy, or polyneuropathy

 

Visceral/Other

Can be referred to the back but is involved in less than 2% of LBP cases

GI, Renal, vascular, or Pelvic conditions can all cause referred pain

 

Psychogenic pain

Chronic pain and psychological distress are often closely related

Concurrent psychiatric diagnosis increases the risk of chronic pain after an acute pain episode

 

Treatment:

Acute lower back pain resolves usually within 4-6 weeks, 70% by 12 weeks.

Best rest should be avoided after 24 hrs

Slow but steady return to activity is the goal

Heat/Cold, simple analgesia, may be enough to control symptoms


Pharmacotherapy:

Paracetamol and NSAIDs are first line treatments

Muscle relaxants have mixed evidence - maybe some help for acute spinal pain but not neuropathic pain

Opioids should be avoided in chronic pain

TCAs are useful for chronic spinal pain as are gabapentinoids, and SNRIs


CAM

These can be useful in the right setting

Massage, TENS, acupuncture, spinal manipulation etc


Exercise

Not helpful in acute pain but has some evidence in chronic pain

 

Interventional Procedures


Epidural steroid injections:

First line option in radicular pain where other therapies have failed

Some studies suggest reduces the need for surgery and works best in patients with intermittent symptoms, limb pain > axial pain, and shorter duration symptoms (< 6 months)

They can help with spinal stenosis though often short lived


Intra/Extra articular corticosteroids:

Useful in SI joint dysfunction but less so for discogenic pain


Trigger point injections

Can be helpful for myofascial trigger points

Dry needling can be trialled


Radiofrequency ablation

Useful for facet and SIJ-mediated pain


Vertebral augmentation

Kyphoplasty or vertebroplasty may be considered for the treatment of acute or subacute vertebral compression fractures that do not respond to medications

Remember in fractures, the facet joints may still play a significant role in pain generation


Percutaneous disc decompression

Alternative to surgery for radicular pain - can provide a year of relief in correct patients


Spinal cord stimulation

Effectiveness compared to conventional management and repeat surgery in the treatment of failed back surgery syndrome associated with radicular symptoms.

Best candidates are those with extremity pain that is worse than axial pain of neuropathic origin

 

Surgery

Outcomes of surgery are best when performed acutely for progressive nerve root injury due to a herniated disc

Refer early if patients have 'red flags'. Certain features require earlier surgical referral such as: Cauda equina syndrome, progressive motor deficits, failed conservative therapies


Decompressive surgery may improve symptoms for up to 6 months in patients with lumbar radiculopathy but most studies show no significant difference after 2 years

Patients with spinal stenosis or significant spondylolisthesis benefits from surgery can last up to 2 years

If chronic axial pain, improvement is only about 15-40% for functional improvement or pain relief

Neck pain - no benefit in surgery over conservative therapy


References:

  1. Murakami E. (2019) Diagnosis of Sacroiliac Joint Disorder. In: Sacroiliac Joint Disorder. Springer, Singapore. https://doi-org.ezproxy.library.sydney.edu.au/10.1007/978-981-13-1807-8_4




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