Sinister Causes of Back Pain

Back pain is very common and usually benign. However, it can sometimes indicate a much more serious underlying disease and it is important to recognise these less common but crucial exceptions.

• Incidence Back pain is so very common that most of us can expect to suffer from it at some time. Systematic enquiry in older people reveals that almost everyone has it but most regard it as a normal accompaniment of 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. Sinister causes become more frequent with rising age.

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.

There are other possible causes for concern:

• Absence of significant trauma to cause pain.
• Pain of gradual onset unrelated to physical activity.
• Morning stiffness and restriction of limitation of back movements in all directions.
• Pain from the pancreas or a posterior duodenal ulcer is upper lumbar, gnawing and tends to be eased by sitting forward leaning on the elbows.
• If the patient writhes with pain this suggests a dissecting aneurysm.

Signs

• 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 that is usually at the bifurcation.

• Primary malignancy of the reticulo-endothelial system of which myeloma is the most likely.
• Osteosarcoma does not usually affect the spine.
• Secondary cancers usually from bronchus, breast, prostate, thyroid and kidney or carcinoma of pancreas.
• Metabolic disease of bone including Paget's disease and osteoporosis leading to vertebral collapse.
• Paget's Disease affects the pelvis in 72% of cases and the lumbar spine in 58%.
• 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. There may be a positive family history, rash of psoriasis, urethritis, peripheral arthritis or inflammatory bowel disease.
• Infection. Never forget tuberculosis. Osteomyelitis can occur. HIV predisposes to infections including tuberculosis. 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. They are indicated only if there is cause for concern and routine investigation will provide a very low return.

Blood and Urine tests

• An abnormal full blood count and ESR or PV may give a non-specific indication that this is not simple back pain.
• LFTs may show an elevated alkaline phosphatase in metastatic disease or Paget's Disease. In the latter biochemical indices of bone turnover like urinary hydroxyproline will be markedly elevated.
• PSA will be raised in carcinoma of prostate.
• Nephrolithiasis may produce red cells in the urine.

Imaging

• Plain x-ray of the back has little to offer in simple back pain⁷ but it delivers 120 times the dose of radiation as a CXR. If sinister causes are suspected it is much more valuable.
• 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 for back problems. 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.

Non-Drug

The management of sinister back pain is to diagnose and treat the cause. If the cause is metastatic carcinoma then radiotherapy may be useful.

Drugs

Analgesia should be given as appropriate.

Surgical

If cauda equina compression occurs the patient must see a neurosurgeon or an orthopaedic surgeon with an interest in backs that same day. Decompression must occur as a matter of urgency to prevent nerve damage becoming irreversible.
Dissecting aortic aneurysm requires surgical repair very soon. The operative mortality from elective surgery is a little under 5% compared with 40% for emergency repair.⁸

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 is 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.