[Subcutaneous botulinum toxin in the treatment of peripheral neuropathic pain]

Neuropathic pain impairs quality of life in affected individuals and poses a challenge to clinicians due to the complexity of its treatment and frequent therapeutic failures. We present 4clinical cases of chronic neuropathic pain (LANSS ≥ 19), refractory to conservative treatment (meralgia paraesthetica, post-surgical pain and 2surgical scars). Subcutaneous botulinum toxin type A was infiltrated periodically over the painful area. All patients experienced subjective improvement in pain and improvement measured by the visual analogic scale. Pain relief started at 5-21 days and continued up to 1.5-3 months, and up to 9 months in one patient. Pain that reappeared was of lower intensity in 3patients and was reduced in area in 2patients.

The potential role of neuropathic mechanisms in dry eye syndromes

Dry eye syndromes can involve both nociceptive and neuropathic symptoms. Nociceptive symptoms are the normal physiological responses to noxious stimuli. Neuropathic symptoms are caused by a lesion or disease of the somatosensory nervous system and can be the result of hypersensitisation of peripheral or central corneal and conjunctival somatosensory nerves. For example, inflammation could induce neuroplastic peripheral sensitisation of the ocular surface or lid wiper and exacerbate nociceptive symptoms. Neuropathic symptoms may explain the incommensurate relation between signs and symptoms in some dry eye syndromes although absence of signs of a dry eye syndrome may also be a consequence of inappropriate methods used when examining for them. Involvement of neuropathic mechanisms may also help explain dry eye symptoms which occur in association with reduced corneal sensitivity. This review includes a discussion of the potential for ocular symptoms involving neuropathic mechanisms to contribute to psychosocial problems such as depression, stress, anxiety and sleep disorders as well as for these types of psychosocial problems to contribute to neuropathic mechanisms and dry eye syndromes. Failure to consider the possibility that neuropathic mechanisms can contribute to dry eye syndromes may reduce accuracy of diagnosis and the suitability of treatment provided. Dry eye symptoms in the absence of commensurate evidence of tear dysfunction, and unsatisfactory response to tear dysfunction therapies should prompt consideration of neuropathic mechanisms being involved. Symptoms which persist after local anaesthetic instillation are more likely to be neuropathic in origin. Reducing inflammation may help limit any associated neuroplastic hypersensitivity.