What key features need to be sought from the history?

What specific features should be sought on physical examination?

What is the diagnosis?

How should the patient be investigated?

An investigation is performed as shown in Figures 52.1–52.3.

Figure 52.1

Figure 52.2

Figure 52.3

What is the investigation and what do the three images show?

A.1 The first aim of the history is to try to distinguish between the major causes of limb pain. These include:

This patient gives a typical account of ‘sciatica’ (which often arises from lumbar disc herniation). It is important to distinguish between radiculopathic pain (‘sciatica’) and non-specific lumbar pain. Radiculopathic pain refers to pain which radiates into the limb in a myotomal distribution. It arises from compression or compromise of particular nerve root(s). This is typically exacerbated by coughing, sneezing or straining. Surgery to relieve nerve root compression (e.g. lumbar discectomy in the presence of a significant disc prolapse) is generally performed with the key aim of improving radiculopathic pain. Non-specific lumbar or back pain may radiate to the buttock and thigh but not usually beyond the knee. It is usually not helped by surgery.

The clinician may also use the patient’s description of radiculopathic pain to deduce the possible nerve roots affected in the majority of patients. For example, an L3 radiculopathy typically results in pain which radiates to the knee. In contrast, an S1 radiculopathy usually causes pain which is felt as far as the ankle/foot. Asking specific questions about the pattern of any sensory changes may further point to specific dermatome(s).

Further history should be directed towards excluding:

A.2 On physical examination evidence should be sought of overall state of health, e.g.:

Specific features referable to the symptoms and the need to be excluded:

A.3 This patient has evidence of cauda equina compression. This is judged by symptoms of acute bladder paralysis and buttock numbness. The clinical examination has revealed a distended bladder, reduced anal tone and numbness in the perineal and buttock regions (S2, 3, 4). There are also signs consistent with S1 nerve root compression (absent ankle reflexes and plantar flexion weakness).

A.4 This is a neurological emergency and any delay in treatment may compromise neurological recovery and result in permanent paralysis. An urgent MRI scan of the lumbosacral spine is the investigation of choice, but may not always be available. A CT scan is the more often performed procedure. In the absence of MRI or CT, a lumbar myelogram can also point to the diagnosis. Plain X-rays are generally unhelpful. Lack of appropriate radiological facilities and neurosurgical expertise should prompt an urgent transfer of the patient to a centre where these are available. Cauda equina compression requires prompt surgery to optimize the chances of neurological recovery. In patients with sphincteric dysfunction (bladder/bowel), the recovery process may take many months and is often incomplete.

Blood tests should be done but must not delay emergency treatment. They are of lesser importance in those patients who otherwise appear in normal health, making a benign aetiology more likely. They can be very important in those with presentations suspicious of a sinister underlying problem, e.g. malignancy. An elevated white cell count or inflammatory markers (ESR, CRP) may suggest infection. Other abnormalities in blood counts, liver function tests, total protein or calcium levels could suggest underlying malignancy. Tumour markers (e.g. PSA) may be helpful. Coagulation studies (INR, APTT) should be performed when there is clinical suspicion of a bleeding diathesis.

A.5 These are MRI scans, with focus on the spinal canal. T2-weighted images show cerebrospinal fluid (CSF) contained within the thecal sac which has a hyperintense (bright) appearance. A compressive lesion (e.g. disc prolapse) is easier to recognize on this sequence.

The sagittal MRI of this patient (Figure 52.1) reveals two problems. First, the patient has a congenitally narrow spinal canal. Any disc prolapse is more likely to cause a cauda equina compressive syndrome. Second, the patient has an L4/5 disc prolapse (Figure 52.2) which explains his clinical presentation. This compresses the thecal sac to the extent that little CSF is visible at this level. This compression leads to compromise of the nerve roots which form the cauda equina. Figure 52.3 is at the level of L3/4 disc and shows the normal appearance of the thecal sac and spinal canal.

Abnormalities involving the vertebral body (e.g. osteomyelitis, metastatic disease) or disc (e.g. infective discitis) will involve careful study of both T1- and T2-weighted MRI sequences. The diagnosis is further aided by post-contrast imaging studies.