Behçet’s, Chiari malformations.
Spinothalamic Tracts
A lesion within these tracts produces changes in pain and temperature sensation below its level. With progressive compression from outside the cord, such as by an enlarging thoracic meningioma (extramedullary cord compression), the sensory level will tend to commence in the feet and rise to the level of the tumour – because of lamination of spinothalamic fibres in the cord. The patient may notice they cannot gauge water temperature with a foot. Extramedullary cord compression tends to affect both principal cord sensory pathways – both posterior column and spinothalamic.
When a lesion is within the cord (intramedullary) such as a syrinx (Chapter 16) sensory loss can initially be confined entirely to the spinothalamic pathways. The sensory loss is described as dissociated. Suspended sensory loss describes another aspect also seen with a syrinx: the dissociated sensory loss does not extend to the lower limbs – it is thus hanging, on the thorax or abdomen.
Sacral sparing is the phrase used to capture preserved sacral and perineal sensation when a central cord lesion expands centrifugally, damaging first centrally placed fibres and reaching last the spinothalamic sacral fibres on the periphery of the cord.
As a cavity develops within one side of the cord, dissociated sensory loss on one side occurs with pyramidal signs such as a spastic lower limb on the other. This carries the eponym Brown‐Séquard, from a treatise in 1849 on traumatic hemisection of cord. Brown‐Séquard findings mean spinothalamic signs on one side with pyramidal and dorsal column signs on the other. They point to a cord lesion, on the same side as the pyramidal and dorsal column loss. The patient may report: ‘I cannot feel the bathwater with my left foot, but it is my right that drags’.
Brainstem Lesions and Sensation
Various patterns are seen: trigeminal sensory loss (Chapters 2 and 13), dissociated (spinothalamic) sensory loss in the limbs, and/or lower limb numbness. The site of a lesion is usually determined more from signs from cranial nerve nuclear damage than by the sensory loss.
Thalamic Lesions
Destructive lesions of the complex thalamic nuclei are relatively unusual causes of sensory symptoms. When the ventral posterior lateral (VPL) and ventral posterior medial (VPM) thalamic nuclei (Chapters 2 and 5) are damaged, such as following a thrombo‐embolic stroke, contralateral hemi‐anaesthesia follows immediately. Sometimes, however, during the weeks or months following the stroke, highly unpleasant disabling persistent pain (post‐stroke central pain, a.k.a. thalamic pain, Chapter 23) develops in partially anaesthetic limbs. Pain is usually permanent.
Mononeuropathy, Polyneuropathy
See Chapters 10, 13, and 16.
Common mononeuropathies are easy to recognise once seen, such as ulnar, median, radial, common peroneal (lateral popliteal), lateral cutaneous nerve of the thigh and sural nerve lesions. Cranial nerves are discussed in Chapter 13.
Multiple mononeuropathy means two or more peripheral nerve lesions. Principal causes are leprosy, diabetes, hereditary neuropathy with liability to pressure palsies (HNPP), and vasculitis such as polyarteritis.
Polyneuropathy a.k.a. peripheral neuropathy describes conditions in which nerves die back, usually symmetrically to cause peripheral (hands and feet) sensory loss, muscle weakness and wasting with loss of tendon reflexes.
Neurogenic Muscle Wasting
The crux is to distinguish between:
Generalised thinning, normal in old age and seen in cachexia – power is normal
Widespread wasting seen in MND, polyneuropathy
Focal wasting with denervation.
Seek out sites of predilection:
Small hand muscles (T1)
Guttering of forearm flexors
Wasted anterior tibial compartment – lateral to the leading edge of the tibia
Wasted extensor digitorum brevis muscles – small oyster‐like muscles below each lateral malleolus.
Muscles with normal bulk, consistency and power are usually normal electrophysiologically and histologically.
Root Lesions
Characteristics are:
Root pain
Wasting and muscle weakness
Sensory loss, and
Loss/depression of deep tendon reflex(es).
A root lesion is often called radiculopathy when this is part of an inflammatory, vascular or neoplastic process with derivatives such as polyradiculomyelopathy. I prefer the shorter English word root. A cervical or lumbar root lesion usually implies compression, often from a disc. Movements, root values, muscles and nerves are summarised in Table 4.4.
Table 4.4 Movement, root value, muscle & nerve.
| Movement | Root | Muscle | Nerve |
|---|---|---|---|
| Shoulder abduction | C5, (C6) | Deltoid (also supraspinatus) | Axillary |
| Elbow flexion (supinated) | (C5), C6 | Biceps | Musculocutaneous |
| Elbow flexion (mid‐prone) | C5, (C6) | Brachioradialis | Radial |
| Wrist extension | (C6), C7, (C8) | Triceps | Radial |
| Tip of thumb & index finger flexion | C7, C8 |
