Treatment of PUVA-induced skin pain with capsaicin

A review on PUVA pricks-A debilitating adverse event

PURPOSE

PUVA phototherapy is indicated for various dermatological conditions. Adverse events due to PUVA phototherapy are seen in a sizable number of patients and can result in therapy cessation. This review will focus on PUVA pricks, an adverse event first reported by Tegner in 1979.

METHODS

Articles were retrieved from PubMed starting from January 1979 until February 2021 yielding 1228 unique articles. Articles were included when they described individual patient characteristics, and patients were treated with PUVA therapy.

RESULTS

After screening, 33 patients were extracted from 9 articles, published between 1979 and 2005.

CONCLUSION

PUVA pricks are paroxysmal episodes of burning or prickling pain, akin to peripheral neuropathy of the unmyelinated C-fibers. Increased excitability of TRPV1 and TRPA1 channels while under PUVA therapy might be a contributing factor. Effective topical treatment options for PUVA pricks are capsaicin 8% cream, urea 4%, or petrolatum emollients. Antiepileptics such as phenytoin, clonazepam, and gabapentin are acceptable oral treatment options. A possible role of N-acetylcysteine in the prevention of PUVA pricks is discussed, though further research is required.

Documento de consenso sobre la modalidad terapéutica del baño-PUVA

Bath PUVA is a variant of phototherapy as efficacious as oral PUVA therapy that avoids many of the adverse effects associated to this treatment. Nevertheless, the special features and the specialized equipment required for its employment have limited its application in the dermatologic clinics of our country. Following the trend initiated after the publication of the consensus document on oral PUVA therapy and narrow band (NB) UVB therapy, the Spanish Photobiology Group from the Spanish Academy of Dermatology and Venereology has developed a therapeutic guideline for bath PUVA therapy based on the literature review and the experience of its members. The document aims to be a practical reference guide for those dermatological centres that include phototherapy among their services. It reviews the concept and indications of this type of treatment and proposes recommendations concerning therapeutic procedures, drug associations of interest and prophylaxis and management of adverse effects.

Treatment of prurigo nodularis with topical capsaicin

BACKGROUND

Prurigo nodularis is an eruption of lichenified or excoriated nodules caused by intractable pruritus that is difficult to treat. Therefore the antipruritic efficacy of capsaicin seemed to be of particular interest because this alkaloid, extractable from red pepper, interferes with the perception of pruritus and pain by depletion of neuropeptides in small sensory cutaneous nerves.

OBJECTIVE

The aim of this concentration- and regimen-ranging study was to evaluate the efficacy, safety, and practicability of capsaicin in the topical treatment of prurigo nodularis in a large series of patients.

METHODS

A total of 33 patients with prurigo nodularis of various origins were selected to receive capsaicin (0.025% to 0.3%) 4 to 6 times daily for 2 weeks up to 10 months. The consecutive follow-up period was up to 6 months. In 7 patients, skin biopsy specimens were taken before, during, and after therapy and investigated histologically, immunohistochemically, and ultrastructurally.

RESULTS

All 33 patients could be evaluated for efficacy. After cessation of the symptoms of neurogenic inflammation, such as burning sensations or erythema, all of them experienced a complete elimination of pruritus within 12 days. In addition, capsaicin largely contributed to the gradual healing of the skin lesions. After discontinuation of the therapy, pruritus returned in 16 of 33 patients within 2 months. At the ultrastructural level, no degenerative changes of cutaneous nerves could be found during or after capsaicin therapy. Depletion of substance P was demonstrated by confocal laser scanning microscopy thus confirming the specific effect of capsaicin in vivo.

CONCLUSION

Topical treatment of prurigo nodularis with capsaicin proved to be an effective and safe regimen resulting in clearing of the skin lesions.

Menthol desensitization of capsaicin irritation. Evidence of a short-term anti-nociceptive effect

Evidence is presented of a short-term antinociceptive effect of menthol that was discovered in the course of investigating menthol's potential to sensitize the mouth to capsaicin. Previous research had shown that treating the tongue with menthol 15 min before exposure to capsaicin could enhance the irritancy of capsaicin, and we wished to learn if this effect would increase as the time between exposure to menthol and capsaicin decreased. We found instead that when capsaicin followed menthol by only 3.5 min, or when it was presented in mixture with menthol for 2-3 min, sensory irritation was reduced rather than enhanced. We examined the duration of this apparent crossdesensitization in a second experiment by varying the delay between exposure to menthol and a block of three consecutive capsaicin stimuli. Cross-desensitization tended to decline as the interstimulus interval (ISI) increased to 5 min, and even when desensitization was maximal, it was significant only for the first of the three capsaicin stimuli. In the final experiment we investigated how menthol self- and cross-desensitization can influence the perception of menthol-capsaicin mixtures. During a series of five, 90-s stimulations, self- and cross-desensitization became evident at the beginning of the second exposure, but the effect on mixture intensity again diminished rapidly as stimulation continued. We infer from these results that method can transiently desensitize capsaicin-sensitive fibers, but that exposure to capsaicin rapidly overrides the effect. The implications these findings have for menthol's potential as a topical analgesic are discussed.