Postherpetic Neuralgia

Background: In the last years, new findings from the research on pain diseases and the enhancement of therapeutic options have drastically changed the treatment of postherpetic neuralgia (PHN). This disease, belonging to the neuropathic pain syndromes, needs an adequate pain therapy at an early stage to prevent pain chronicity. Definition and Clinical Attributes of PHN: In 20% of all cases of herpes zoster, the innervation territory of the trigeminal nerve is affected. A PHN exists by definition in the case of persisting pain in the zoster-affected area 6 months after healing of the zoster eruptions. The incidence of PHN depends on the patient's age: 50-75% of patients in the seventh decade develop PHN after an infection with herpes zoster. The clinical appearance of PHN is characteristic. Three different pain types can be distinguished: 1. spontaneous, constant, burning pain, 2. intermittent sharp, lancinating pain and 3. pain in response to a normally non-painful stimulus (mechanical allodynia). Other phenomena which can be observed are hyp- or anaesthesia, hypalgesia and par-or dysaesthesia. Pathophysiology of Neuropathic Pain: In the last few years, pathomechanisms of individual pain symptoms occuring in PHN have been identified. These include peripheral and central sensitisation as well as spontaneous activity of damaged afferent nociceptive fibres as the consequence of changes in channels on the neuron's membrane. Treatment of PHN: A basic rule in the treatment of neuropathic pain syndromes is that the medication should be taken for at least 2-4 weeks before making a final evaluation. Systematic reviews of data from clinical trials of drug therapy for PHN have given distinct indications for antidepressants, antiepileptics, opioid analgesics and topically acting agents. Tricyclic antidepressants act on CNS pain-modulating descending pathways. The antiepileptics gabapentin and pregabalin act on calcium channels on presynaptic terminals of afferent nociceptive neurons in the central nervous system. Carbamazepine and oxcarbazepine may be helpful for some patients, but there is still a lack of controlled trials demonstrating efficacy in the treatment of PHN. Oral oxycodone and tramadol are verifiable effective drugs in PHN. Topically acting agents with verifiable efficacy in PHN are capsaicin and lidocaine, both available in the form of patches for local use.