Reduction in touch sensitivity and hyperinnervation in vesicant-injured rabbit eyelid by direct injection of corticotropin releasing factor

Dynamic mechanical allodynia following finger amputation: Unexpected skin hyperinnervation

The development of chronic pain after amputations is not an uncommon event. In some cases the most disabling problem is represented by the symptom called dynamic mechanical allodynia, characterized by the painful sensation evoked by gently stroking the skin. Despite the growing interest in understanding pain mechanisms, little is known about the mechanism sustaining this peculiar type of pain. We present here the case of a 53-year-old female patient who complained of severe tactile allodynia in the hand after amputation of her left second finger, resistant to several medical and surgical treatments. In order to gain information about the pain mechanism, two neurodiagnostic skin biopsies were obtained from the area of tactile allodynia and from the contralateral, normal skin area. Skin biopsies showed an unexpected increased innervation of the allodynic skin compared to the contralateral, normal skin area (+ 80.1%). Hyperinnervation has been proposed as a mechanism of pain following nerve lesions, but the increased innervation described here could be also attributed to neuronal plasticity occurring in chronic inflammatory conditions. Independently from the uncertain cause of the epidermal hyperinnervation, in this patient we tried to reduce the elevated number of epidermal nerve fibres by treating the skin with topical capsaicin (0.075%) three times a day, and obtained a persistent pain relief. In conclusion, neurodiagnostic skin biopsy might represent an useful tool for detecting derangements of epidermal innervation in patients with dynamic mechanical allodynia and can help to select an individually tailored therapeutic strategy in such difficult clinical conditions. Further studies are needed to clarify this issue and try to gain better understanding of chronic pain mechanisms in patients who underwent finger amputation.

Modulating neuromuscular junction density changes in botulinum toxin-treated orbicularis oculi muscle

PURPOSE

Botulinum toxin A is the most commonly used treatment for blepharospasm, hemifacial spasm, and other focal dystonias. Its main drawback is its relatively short duration of effect. The goal of this study was to examine the ability of corticotropin releasing factor (CRF) or antibody to insulin growth factor I-receptor (anti-IGFIR) to reduce the up-regulation of neuromuscular junctions that are associated with return of muscle function after botulinum toxin treatment.

METHODS

Eyelids of adult rabbits were locally injected with either botulinum toxin alone or botulinum toxin treatment followed by injection of either CRF or anti-IGFIR. After one, two, or four weeks, the orbicularis oculi muscles within the treated eyelids were examined for density of neuromuscular junctions histologically.

RESULTS

Injection of botulinum toxin into rabbit eyelids resulted in a significant increase in the density of neuromuscular junctions at one and two weeks, and an even greater increase in neuromuscular junction density by four weeks after treatment. Treatment with either CRF or anti-IGFIR completely prevented this increase in neuromuscular junction density.

CONCLUSIONS

The return of function after botulinum toxin-induced muscle paralysis is due to terminal sprouting and formation of new neuromuscular junctions within the paralyzed muscles. Injection with CRF or anti-IGFIR after botulinum toxin treatment prevents this sprouting, which in turn should increase the duration of effectiveness of single botulinum toxin treatments. Future physiology studies will address this. Prolonging botulinum toxin's clinical efficacy should decrease the number of injections needed for patient muscle spasm relief, decreasing the risk of negative side effects and changes in drug effectiveness that often occurs over a lifetime of botulinum toxin exposure.