Central Neuropathic Pain

Pain arising directly from a lesion or disease affecting the somatosensory nervous system at the level of the spinal cord or brain, distinct from peripheral neuropathic pain and from nociceptive pain, with mechanisms and treatment approaches that overlap substantially with, but are not identical to, peripheral neuropathic pain syndromes.

Causes

Central post stroke pain follows cerebrovascular events affecting the spinothalamic pathways, classically involving the thalamus though occurring with lesions at multiple levels of the central pain pathway.

Spinal cord injury pain occurs both at the level of injury (segmental) and below the level of injury, reflecting disruption of ascending sensory pathways and subsequent maladaptive central reorganisation.

Multiple sclerosis produces central neuropathic pain through demyelinating lesions affecting sensory pathways, presenting as continuous burning dysaesthesia or as paroxysmal neuralgic pain (trigeminal neuralgia being a recognised manifestation in this population).

Syringomyelia, spinal cord tumours and other structural central nervous system lesions are less common but important causes requiring specific investigation and, where possible, treatment of the underlying structural pathology.

Pathophysiology

Disruption of the spinothalamic and related sensory pathways produces disinhibition and maladaptive reorganisation of central pain processing circuits, with loss of normal inhibitory control and the development of abnormal spontaneous neuronal activity within the deafferented pathway, producing pain in the absence of an ongoing peripheral noxious stimulus.

Spontaneous, continuous burning, aching or freezing pain, frequently accompanied by paroxysmal shooting or electric shock like exacerbations, characterises the pain quality across most central neuropathic pain syndromes.

The distribution of pain corresponds to the region of somatosensory representation affected by the causative lesion rather than to a peripheral nerve or dermatomal distribution, which can appear confusing or anatomically implausible if this underlying principle is not appreciated.

Allodynia and hyperalgesia are common, with pain frequently triggered or worsened by touch, temperature change or emotional stress.

Onset may be immediate following the causative event (such as spinal cord injury) or delayed by weeks to months (as is typical in central post stroke pain), an important point for patient counselling since delayed onset pain may not initially be attributed to the preceding neurological event.

Associated sensory abnormalities (numbness, altered temperature sensation) in the affected region often coexist with the pain, reflecting the underlying sensory pathway disruption.

Significant impact on mood, sleep and function is common given the chronic, often severe and treatment resistant nature of central neuropathic pain.

Diagnosis is clinical, based on a history of a causative central nervous system lesion or disease, a compatible pain distribution and quality, and the presence of sensory abnormalities on examination corresponding to the region of somatosensory pathway involvement.

Magnetic resonance imaging of the brain or spinal cord, as appropriate to the suspected level of the lesion, confirms the underlying causative pathology (stroke, demyelination, syrinx, tumour, cord injury) and is essential both to establish the diagnosis and to exclude other treatable structural causes.

Quantitative sensory testing, where available, can characterise the specific pattern of sensory loss and gain (thermal, mechanical) and support the diagnosis, though it is used predominantly in specialist and research settings rather than routine clinical practice.

Careful examination to distinguish central neuropathic pain from musculoskeletal pain, spasticity related pain and peripheral neuropathic pain (which can coexist, particularly in spinal cord injury) is important since management approaches differ.

Exclude other potentially treatable causes of new or worsening pain in a patient with an established central nervous system lesion, including syrinx progression, new structural pathology or a complication such as spasticity or pressure injury in spinal cord injury patients.

Gabapentinoids (pregabalin, gabapentin) and tricyclic antidepressants (amitriptyline) are first line pharmacological agents, with evidence specifically supporting their use in central post stroke pain and spinal cord injury pain, titrated gradually to balance efficacy against sedation and other dose limiting adverse effects.

Serotonin noradrenaline reuptake inhibitors (duloxetine) offer an alternative or adjunct, particularly where coexisting depression is present.

Combination therapy, using agents from different classes at moderate doses, is often more effective and better tolerated than escalating a single agent to maximum dose, mirroring the general approach to neuropathic pain management.

Lamotrigine has specific evidence in central post stroke pain, and may be considered as an additional or alternative agent particularly where other first line options have been ineffective or poorly tolerated.

Opioids generally offer limited benefit in central neuropathic pain and carry substantial risk with long term use, and are not recommended as routine therapy, though may have a limited role in carefully selected, closely monitored cases where other options have failed.

Non pharmacological measures, including physiotherapy, transcutaneous electrical nerve stimulation, and psychological support (cognitive behavioural therapy, given the substantial impact of chronic pain on mood and coping), form important adjuncts across all central neuropathic pain syndromes.

Spinal cord stimulation and, in highly selected refractory cases, motor cortex stimulation or deep brain stimulation are considered by specialist pain and neurosurgical services for severe, treatment resistant pain, though evidence and availability vary considerably.

Address and treat spasticity, contractures and other coexisting complications in spinal cord injury and multiple sclerosis populations, since these can both cause independent pain and exacerbate the perception of central neuropathic pain.

Set realistic expectations with the patient regarding the goal of pain reduction and functional improvement rather than complete resolution, given the generally chronic and only partially treatment responsive nature of central neuropathic pain, with ongoing specialist pain service involvement for complex or refractory cases.