Sinister Causes of Back Pain

Back pain is very common and usually benign. This is covered in the article entitled Back pain-non sinister causes. Our record Back Pain in Children covers the different causes of back pain found in younger patients.

However back pain can sometimes indicate a much more serious underlying disease and it is important to be alert to these uncommon but serious causes of back pain.

Incidence

Back pain is so common that everyone can expect to suffer from it at some time. The elderly often regard it as part of normal ageing and so do not complain. Between the ages of 25 and 64 the annual incidence is said to be 4.7% with a 59% chance of a lifetime occurrence.¹

Prevalence

At any given time the number of people affected by back pain will be between 4 and 33%.²
The lifetime prevalence of low back pain is reported as over 70% in industrialised countries (one-year prevalence 15% to 45%, adult incidence 5% per year). Peak prevalence occurs between ages 35 and 55.³
Most of this will be simple back pain and not sinister in significance. However it is worth contrasting this with figures for primary care which indicate:³

• Sinister causes become more frequent with rising age.
• About 4% of people with low back pain in primary care have compression fractures.
• About 1% of people with low back pain in primary care have a neoplasm.
• Ankylosing spondylitis and spinal infections have a prevalence of less than 1% .
• The prevalence of prolapsed intervertebral disc is between 1% and 3%.

Symptoms

Benign back pain is usually worse on arising in the morning and improves with activity. Failure to follow this pattern suggests a sinister cause. Benign back pain is usually in the lower lumbar region.
There are a number of symptoms and features in the history that should raise concern. The European guidelines for the management of acute back pain in primary care³ lists a number of "red flags":

• Age of onset less than 20 years or more than 55 years
• Recent history of violent trauma
• Constant progressive, non mechanical pain (no relief with bed rest)
• Thoracic pain
• Past medical history of malignant tumour
• Prolonged use of corticosteroids
• Drug abuse, immunosuppression, HIV
• Systemic illness, particularly with loss of weight is indicative of malignancy or possibly infection
• Unexplained weight loss
• Widespread neurological symptoms (including cauda equina syndrome)
• Structural deformity
• Fever

Signs

Examination of patients with back pain is covered in articles on Back Examination, Backache and its Assessment and Neurological Examination of the lower limbs.

• The back should be examined looking for muscle spasm and scoliosis. Range of movements is assessed.
• Check straight leg raising, femoral nerve stretch and local tenderness. Asymmetrical tendon reflexes, muscle wasting or fasciculation suggests that something is impinging on a nerve. The straight leg raising test as a means of diagnosing herniated disc is limited by low specificity.⁶
• If there is any disturbance of bladder function check sensation in the S2,3,4 region and there may be laxity of the anal sphincter.
• If the patient complains of back pain but examination of the back is essentially normal it may indicate an origin outside the axial skeleton including the pancreas or aorta. The abdomen should be checked for tenderness and examined for a pulsating aortic aneurysm (usually arises at the bifurcation of the aorta).
• Neurological signs or symptoms should raise concern.

• Malignancy:
  • Secondary cancers are a more common cause of back pain than primary cancers. These usually originate from bronchus, breast, prostate, thyroid, kidney or pancreas.
  • Primary malignancy of the reticulo-endothelial system (myeloma is the most likely). Osteosarcoma can cause back pain but this does not usually affect the spine.
• Metabolic disease of bone:
  • Paget's disease affects the pelvis in 72% of cases and the lumbar spine in 58%
  • Osteoporosis (leading to painful vertebral collapse)
• Inflammatory disease:
  • Ankylosing spondylitis tends to present slowly in men under 40. The back is very rigid. The condition is very much aggravated by inactivity and helped by exercise.
  • Psoriatic arthritis (rash or family history of psoriasis)
  • Reiter's syndrome (symptoms including urethritis)
  • Arthritis associated with inflammatory bowel disease (usually arthritis is peripheral)
• Infection:
  • Tuberculosis (can be overlooked). Osteomyelitis can occur.
  • HIV predisposes to infections (including tuberculosis)
  • Renal tract infection (pyelonephritis can also cause referred back pain)
• Causes from outside the spinal column include:
  • Dissecting aortic aneurysm
  • A posterior duodenal ulcer, presenting as back pain (may be difficult to diagnose). If an ulcer presents for the first time over the age of 40 gastric malignancy needs to be excluded.
  • Nephrolithiasis can cause back pain

Simple back pain does not require any investigations. Guidelines have been produced in part to prevent unnecessary investigation.^3,7 They are indicated only if there is cause for concern and routine investigation will provide a very low return.

The history and examination should identify 'red flags' or factors which should alert to significant underlying pathology. Investigations should be targeted according to these initial findings. Examples include those listed below.

Blood and urine tests

• An abnormal full blood count and ESR may confirm the need for further investigation.
• LFTs may be helpful. For example alkaline phosphatase can be elevated in:
  • Metastatic disease
  • Paget's disease
• PSA will be raised particularly in carcinoma of the prostate
• Urine tests:
  • Urinary hydroxyproline will be markedly elevated (with increased bone turnover) in Paget's disease
  • Nephrolithiasis may produce red cells in the urine

Imaging

Investigation should again be targeted to patients with significant symptoms or abnormal intermediate investigations.

• Plain x-ray of the back has little to offer in simple back pain⁸ but it delivers 120 times the dose of radiation of a CXR. If sinister causes are suspected it may be indicated.
• Paget's Disease may be seen or metastatic lesions. Those from prostate are sclerotic, those from lung, thyroid and kidney are osteolytic and those from breast may be either.
• Lesions below 2cms diameter may not be seen on plain x-ray but a scintillation scan with ^99mTc is much more sensitive.
• MRI gives a good picture of soft tissues including discs and anything impinging on nerves or spinal cord. Nowadays, many practices have direct access to MRI. There is usually a local protocol to follow. Features of corda equina compression do not merit referral for MRI. They demands same day referral to a neurosurgeon who will arrange an immediate MRI.
• CXR may show primary or secondary carcinoma or pulmonary tuberculosis.
• Ultrasound will show renal stones and is the best way to visualise the pancreas. It can also give a good picture of an aneurysm allowing it to be measured accurately and to detect possible dissection.
• Endoscopy may confirm a posterior ulcer and allow tests for H pylori or malignancy.

The management of sinister back pain is essentially prompt diagnosis and treat of the cause where indicated. Treatment will depend on the cause and may be curative or palliative.

Drugs

A variety of drugs may be used, again depending on the cause of pain. Examples include:

• Analgesics for pain
• Antibiotics for infections
• Anti-inflammatory drugs
• Disease specific drugs. Examples include:
  • Arthritis.
  • Peptic ulcer disease
  • Cancer chemotherapy

Non-drug

• Surgery. Examples:
  • Surgery can be curative for benign causes of cauda equina surgery (if delays are avoided).
  • Dissecting aortic aneurysm requires urgent surgical repair. The operative mortality from elective surgery is a little under 5% compared with 40% for emergency repair.⁹
• Radiotherapy:
  • In metastatic carcinoma radiotherapy can reduce pain.

Referral

Sinister causes of back pain will usually require appropriate referral. Referral may be for diagnosis, for treatment or both and may often be urgent. Discussion with the specialist in advance of referral may assist appropriate direction of the referral and save time for the patient.

Failure to diagnose cauda equina syndrome and to take immediate action may lead to long term neurological damage.
Other sinister causes of back pain may have a fatal outcome. The prognosis may be improved by early and effective intervention.

This depends entirely on the diagnosis. Metastatic carcinoma and carcinoma of pancreas usually have a very poor prognosis but in carcinoma of prostate recent innovations like goserelin have had a profound effect on outcome.