Chronic pain is a common presentation in primary care and can be very difficult to manage. It is generally multifactorial and often it will involve a psychological element to it. The difficulties in management arise from deciding the aetiology of the pain. If a causative factor is found, then tailoring the treatment to the ideas, concerns and expectations of the patient can be difficult. Treatments must be chosen after careful discussion with the patient around potential side-effects and what the patient may expect from the medicine being started.
Central and peripheral pain
- Central neuropathic pain can result from lesions within the spinal cord, for example in MS and spinal cord injury. Certain types of stroke may also cause this.
- Peripheral neuropathic pain arises from lesions affecting peripheral nerves. This may be as a result of trauma, tumour, diabetic neuropathy, idiopathic painful peripheral neuropathy, certain medications such as cytotoxic agents, infection such as HIV, herpes zoster virus, vitamin b12 deficiency or nerve root compression.
The pain is thought to arise from upregulation of sodium channels and activation of NDMA pathways.
Describing the pain
Patients will often use the terms "burning", "shooting", "stabbing" or "sharp" to describe the pain in comparison to nociceptive pain, which is often described as a "dull ache" or "throb".
Examination findings may reveal allodynia, where stroking the affected area may provoke pain. Often patients may report this in terms of bed sheets or items of clothing against their skin causing pain.
The patient’s expectations
Chronic pain results in suffering and lost working days within the economy, therefore there is a significant cost implication. It is important to explain to patients, where you think the pain is originating from, what the treatment options may be and an explanation of the natural progression of the pathology. This is to avoid unrealistic expectations, which may result in further suffering and also significant cost to the NHS. It is important to be alert to depression in patients with chronic pain.
Neuropathic pain can be managed as with nociceptive pain, using the WHO analgesic ladder, however there are a number of different options available to target neuropathic pain.
Tricyclic antidepressants can be used and the commonest used in practice for neuropathic pain is amitriptyline. This is thought to block sodium channels. It is often used at night due to its sedative effect but ‘tea-time’ dosing can be encouraged to avoid ‘hangover effects’ the next morning. Doses can also be split. It is important to warn patients about side-effects, such as dry mouth and blurred vision, before commencing the drug. Start at lower doses to minimise the chance of side-effects and review patients before escalating doses. This can be done face to face or via telephone consultations. Doses that will improve pain are normally around 50mg.
Gabapentin (an antiepileptic drug) is another commonly used neuropathic analgesic. The titration of this is slightly more complex and requires a slow titration over a few days. This generally needs to be written out for patients to avoid incorrect dosing particularly in those patients with polypharmacy. Side-effects include drowsiness, headache, blurred vision and diarrhoea or constipation. Maximum dose is generally 3600mg split in three divided doses. If this drug must be stopped, then a wean over a few weeks may be necessary.
Pregabalin may be useful for those who do not tolerate gabapentin. It does not require titration and effects are generally noticed after a week. It is slightly more expensive to use, however. It is also used for anxiety thus may be helpful if there is an existing anxiety component.
There are a number of other analgesics available for neuropathic pain, including carbamazepine (first line for trigeminal neuralgia), duloxetine (newer agent, now licensed for diabetic peripheral neuropathy) and lidocaine patches, which may be used in postherpetic neuralgia. Capsaicin cream may be used as a topical agent. It is important to warn patients that this may cause transient burning, however this should settle down. Non-pharmacological treatments to consider include TENS machines, acupuncture and physiotherapy.
Where possible, encourage regular review until the patient is stabilised on the maximum tolerated dose. Check concordance and importantly check for side-effects that may affect day to day function, particularly activities such as driving or use of heavy machinery. Augmentation of medications may be necessary. Mediboxes with complicated dosing regimens may also enhance concordance, particularly in the elderly.
It may be necessary to involve a local pain service to provide alternative newer treatments depending on the aetiology of the pain, such as spinal cord stimulators or facet joint injections. They may also provide psychological work around pain via CBT or group work.
Dr Singh is a GP in Northumberland