Chronic back pain: Identifying a neuropathic component

A focused neurological examination based on the history should help determine the origin of back pain, writes Dr Pipin Singh

A detailed history and examination are essential in back pain (Photograph: Jason Heath Lancy)
A detailed history and examination are essential in back pain (Photograph: Jason Heath Lancy)

Lower back pain is a common presentation in primary care. It has a number of aetiologies. A careful history and examination is important to exclude a more rare sinister cause of lower back pain.

A careful history should include and take into account the following:

  • Age of the patient 
  • Have they experienced this problem before? 
  • The location of the pain 
  • The onset of the pain 
  • What triggered the problem? 
  • Does it radiate anywhere else? 
  • Are there any aggravating or relieving factors? 
  • Has the patient already tried any analgesia and if so has this helped? 
  • Are there any associated symptoms? 
  • Has there been any change in perianal sensation? 
  • Has there been any reported numbness or weakness of the legs? 
  • Has there been any paraesthesiae in the legs? 
  • Have they noted a change in bowel or bladder function? 
  • Is there a history of malignancy? 
  • Has the patient noted any night sweats, fever, or unexplained weight loss? 
  • Is there a history of steroid use or TB? 
  • How is this limiting the patient day to day?  

 

It is essential to take a detailed occupational history. Did this problem commence at work and if so is it aggravated by any particular task performed at work? This is likely to influence the clinician’s management and will enable advice to be tailored around this. The patient’s occupation may have implications for the choice of analgesia. Treatment options such as physiotherapy may well be available through their work and signposting to occupational health may be appropriate to address the underlying reason for the problem.  

Is there a neuropathic element?

Neuropathic pain involves the nervous system, whether it is the central or peripheral nervous system. It is thought to be due to upregulation of sodium channels and possible activation of NDMA pathways, though this is one of a number of theories that have been postulated.

Patients will often describe the pain as "sharp", "shooting", or burning" in contrast to nociceptive pain, which is often described as an "ache" or a "throb".

In order to identify whether back pain has a radicular element to it, pay close attention to the following symptoms in the history:

  • Numbness
  • Paraesthesiae
  • Lower limb weakness
  • Change in perianal sensation
  • Bowel or bladder disturbance.
  • Is there any history of disc prolapse or previous imaging such as MRI scans available?
  • Has there been any response to analgesics targeted at neuropathic pain?

 

Neurological examination

With regards to the examination, a focussed neurological examination based on the history should allow one to decipher where the lesion originates.

Note the patient's gait on entry. Examine the power of the lower limbs, proximally and distally (myotome assessment) Test the knee and ankle reflexes if the history suggests so. An assessment of sensation in the appropriate dermatomes will provide more clues as to a possible diagnosis. It may be appropriate to test perianal sensation, anal tone and palpate the bladder if cauda equina is suspected. 

Examination findings suggesting a neuropathic cause of the pain (i.e. a prolapsed disc) may reveal reduced power in the lower limbs, loss of sensation in a specific dermatome, or a reduced or absent knee or ankle reflex. There may be evidence of allodynia (provoking the pain in the area affected by stroking it). A loss of perianal sensation, reduced anal tone, or palpable bladder must be treated as a neurosurgical emergency.

Not all back pain assessments will require all of these examinations. It is important to focus the examination as per the history as the majority of lower back pain is non-specific.

It is important to identify the yellow flags in patients with chronic back pain, which limit the return to normal function. Back pain is a common reason for lost working days and a significant cost to the economy, therefore a positive approach to it is crucial. It may be that there is a more complex psychosocial problem limiting the recovery of the patient and acting as a significant barrier to rehabilitation.

Pharmacological treatment options

The WHO pain ladder applies here, as with any pain, however there are a number of other medications that may be considered in primary care and may be more suitable for the patient due to occupation, previous intolerances or a fear/dislike of certain types of drug.

  • Tricyclic antidepressants - amitriptyline can be used. For effective pain control, 50-75mg is necessary. It has a number of side-effects and starting at a lower dose and building up is sometimes better tolerated by the patient. Tea-time dosing can avoid ‘hang over’ effects and split dosing is also a possibility.
  • Gabapentin can be used. This requires a slow titration over a 2-3 week period approaching 1,800mg total daily dose. There is only a 60% bioavailability of gabapentin at 1800mg. This needs to be weaned if stopping.
  • Pregabalin is another option but is more expensive. It does not require titration, is generally effective after a week and useful if patients have failed to respond to gabapentin.
  • Carbamazepine is an option and first line for trigeminal neuralgia. It works by blocking sodium channels.
  • Duloxetine is also an option.

Non-drug treatments

  • Physiotherapy
  • TENS machine

It maybe appropriate to refer the patient for consideration of surgical options, such as facet joint injections. The options available will often depend on the cause of the pain.

 

Dr Singh is a GP in Northumberland

 

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