Treatment of postscabies prurigo with diflucortolone and chlorquinaldol in a group of African refugees

Introduction

The term ‘postscabies prurigo’ (PSP) is suggested in place of ‘postscabietic nodules’, because this may be considered a true prurigo with known aetiology.^1,2 PSP is a rare complication of scabies. In an Indian study, it occurred in 29/544 patients (5.3%) previously affected by scabies. ³ PSP is caused by a delayed, chronic hypersensitivity reaction to unknown antigens of the mite.^4–9

The diagnosis of PSP requires all the following criteria to be present: (2) a history of scabies which has been successfully treated; (2) round, reddish-brown, papulo-nodular lesions (also in un-typical locations of scabies); (3) complaints of severe itching; (4) absence of mites or parts thereof, eggs and scybala on microscopic, dermatoscopic and histopathologic examinations; (5) ineffective specific anti-scabies therapy; and (6) persistence of the disease for weeks or months. ⁵

PSP is more frequent in men^3,4 and children.^3,5,6,10,11 Recovery may occur with the use of potent topical or intralesional corticosteroids.^5,7,12,13 Pimecrolimus ¹⁴ and tacrolimus^12,15 are sometimes effective. Cryotherapy ¹⁶ and surgical excision ¹³ have also been used.

Patients and methods

Eighteen African refugees (15 men, 3 women; age range 18–46 years; mean age = 31.8 years) were enrolled between March and September 2018. These patients arrived from Niger, Mali, Senegal, Gambia, Guinea, Eritrea and Somalia. All patients had been affected by scabies confirmed by microscopic examination: the latter were considered positive when adult mites (Sarcoptes scabiei var. hominis) or fragments thereof or their eggs or scybala were visible. All patients had been treated according to a regimen previously recommended (5% permethrin cream: one application daily for two consecutive days, the treatment being repeated 7–10 days later). ¹⁷ The diagnosis of PSP was made through negative microscopic and dermatoscopic examinations. Of the 18 patients, 13 had been previously, although unsuccessfully, treated with 0.05% clobetasol proprionate cream (two applications/day on each lesion for two weeks). This treatment was used because it is usually effective, cheaper than pimecrolimus and tacrolimus, and technically easier to use than intralesional corticosteroids, cryotherapy or surgical excision. All patients were therefore treated with a mixture of 0.1% diflucortolone valerate and 1% chlorquinaldol cream (two applications daily on each lesion for two weeks). No other topical or systemic drug was used. The primary objective of the study was the evaluation of itching at the end of the second week of treatment. Itching severity was evaluated by means of a visual analogue scale (VAS) of 0–100. ¹⁸ Secondary endpoints were the changes of morphology of the lesions at the end of the second week of treatment.

Results

Fifteen patients (83.3%) could be evaluated. All reported improvement of itch: before the beginning of treatment, the mean VAS was 86/100; at the end, it was 29/100 (−57/100). In 6/15 patients (40%), a mild improvement of the lesions was observed: they appeared less infiltrated. No systemic or local adverse events were reported or observed. Six of 15 (40%) judged the smell of the cream as rank.

Discussion

Chlorquinaldol, or hydroxydichloroquinaldine (5,7-dichloro-2-methyl-8 - quinolinol), is a derivative of 8-hydroxyquinoline. It showed good activity, both in vitro and in vivo, against yeasts, dermatophytes, Gram-positive bacteria, Neisseria gonorrhoeae and Chlamydia trachomatis.^19–24 In a recent study, staphylococci were the most sensitive bacteria to chlorquinaldol, with MIC values in the range of 0.016–0.5 mg/L. A lower activity was observed against Gram-negative bacteria: 77% of the isolates were inhibited at concentrations in the range of 128–512 mg/L. Chlorquinaldol showed a bactericidal activity after 24–48 h of incubation. ²⁵ Furthermore, an important anti-pruritic action of chlorquinaldol is hypothesized.^26,27

A limitation of our study is the small number of patients; however, as previously mentioned, PSP is a rare complication of scabies. Our results suggest: (1) the association diflucortolone/chlorquinaldol may be useful for the treatment of itch in PSP; (2) this anti-pruritic action may be also due to chlorquinaldol. Its presence is important, because 13/18 patients had been previously, although unsuccessfully, treated with clobetasol; a synergistic anti-itch action of chlorquinaldol with diflucortolone is, however, possible; (3) at the end of the treatment, a mild improvement of infiltration of the lesions was observed; and (4) thanks to the antibacterial action of chlorquinaldol, the association between diflucortolone and chlorquinaldol may also be useful to prevent bacterial superinfection in scabies and PSP. ²⁸