Successful treatment of nodular scabies with long-lasting ivermectin dose schedule in an adult patient non responder to permethrin

Abstract

Scabies is a worldwide diffused ectoparasitic infestation of the skin by the mite Sarcoptes scabiei: classic scabies is the most common form while the nodular form is a rare clinical variant characterized by the highly itchy nodules and papules. This report describes the clinical approach of a case of late diagnosis of nodular scabies non responder to treatment with permethrin applied twice. Given the non-response, the decision was made to start ivermectin along with tacrolimus ointment. The lesions improved after the second ivermectin dose and pruritus disappeared; on the basis of the clinical history the drug schedule was tailored and a total of 17 doses were administered till the last follow-up visit (June 2025): no side effect was reported. Nodular lesions gradually disappeared leaving hyperchromic lesions occasional flared up with burning sensation and were treated on demand with topic aloe. This report suggests that a personalized and long-term ivermectin schedule can be successful in selected cases of nodular scabies with previous resistance to permethrin.

Highlights

• •Nodular scabies is a rare clinical variant.
• •Resistance to permethrin is an escalating threat.
• •Ivermectin is a well-tolerated drug: multiple ivermectin doses are used in a short interval for the crusted form.
• •A patient with nodular scabies resistant to permethrin was treated with a personalized long-lasting ivermectin schedule.
• •The drug was safe and effective and a tailored regimen can be an option in selected patient.

Introduction

Scabies is an ectoparasitic disease included in the list of neglected tropical diseases and an important health issue in tropical Latin America, Asia and Oceania, but the incidence is increasing in Western countries. Many factors may be involved in this changing epidemiology, included delayed or even missed diagnosis and therefore late or no treatment at all: common morphologic features of scabies are itchy erythematous papules, often excoriated, that mimic those of other skin conditions and make difficult to identify the burrow, the pathognomonic lesion [1]. Besides the classic form of the disease, there is an uncommon clinical variant called nodular scabies characterized by pruritic inflammatory papules and nodules: here we report the case of a young immunocompetent man who experienced a long-lasting nodular scabies needing a long-term ivermectin dose schedule and topical tacrolimus to achieve a definite cure.

Case

A mid thirty European man presented to his General Practitioner in June 2024 with skin lesions in the inguinal, scrotal, and axillary areas. The only clinically relevant data in his medical history was allergy to dust, pollens and other environmental allergens. He reported having travelled to Bangkok in March, where he avoided risky sexual contacts and stayed in a high-quality hotel, where he received a relaxing massage. He denied taking conventional medications and/or herbal products and the previous occurrence of similar skin lesions. After coming back to Hong Kong, where he resided, two weeks later he experienced a widespread itching over the entire body, more intense at night and particularly in the interdigital spaces, axillary folds, and inguinal regions. Subsequently, an erythematous rash and small reddish papules appeared in these areas. Assuming it was atopic dermatitis, the patient took cetirizine for seven days. However, as symptoms worsened and his partner developed similar symptoms, he consulted a local dermatologist. A diagnosis of scabies was made (Fig. 1 and Fig. 2), and daily applications of corticosteroid cream, oral antihistamines, and permethrin 5 % cream were prescribed both to the patient and to the partner: the topic treatment was applied on 7th and 14th May. The treatment was successful in the partner, who had no more contact with the patient while in the latter, after the second application, burrows and new vesicles appeared, and the preexisting papules enlarged and became inflamed. Then, a diagnosis of post-scabies eczema was made by the same dermatologist, and topic treatment with clobetasol propionate cream twice daily was prescribed, but its use worsened the lesions. At the second follow-up, on 4th June (24 days after the second permethrin application), he was diagnosed with post-scabetic syndrome: tacrolimus ointment 0.03 % twice was prescribed, which reduced itching but increased the severity and number of skin lesions over the next 2–3 days and therefore the treatment was stopped. Upon returning to Italy in mid-June, on advice from his general practitioner and from an infectious disease specialist, the patient was visited by a dermatologist who identified an ectoparasite in a nodular lesion with dermoscopy, diagnosing nodular scabies. Treatment with ivermectin 0.2 mg/kg was prescribed: the first two doses were assumed at a week interval, the following three doses with a 10-day interval. After this first cycle the drug was assumed every three weeks till October 2024 and then monthly till the last follow-up visit (June 2025). After the second dose of ivermectin, the pruritus completely resolved, and nodular lesions gradually cleared, leaving hyperchromic areas which flared up with a burning sensation at intervals ranging from 20 to 40 days. No further detection of ectoparasite reported after the treatment start. At the time of ivermectin treatment start the patient discontinued clobetasol and continued tacrolimus ointment for about one month: later on, treatment with topic aloe was assumed when skin lesion burning occurred. No side effect related to the ivermectin long-term schedule was reported.

Fig. 1.

Burrows on the right hand.

Fig. 2.

Burrows on the left axillary folds.

Discussion

Nodular scabies is a multifaceted clinical entity and the possible main pathogenetic mechanism is a persistent immune response to mite antigens: the management of the patient affected by this scabies form is challenging because of the need to treat at time both the infection and the inflammatory response (mainly based on eosinophils and mast cells) [2].

When the diagnosis of scabies was first made in this patient the prescribed treatment was permethrin: this topic drug was reported to be effective as monotherapy [1] but in this case the patient experienced a worsening of the skin lesion after the second application. Available data do not allow to identify a definite etiology for: a side effect of the treatment as skin irritation associated to drug-resistant scabies is a possible explanation. A speculative option may be eosinophils prevalence in the scabies nodules, a characteristic previously described in non-responder subjects [3]. Of note, we have no definite explanation to why permethrin did not work in our patient but it worked in the partner: an unintentional incorrect application might have occurred or, maybe, drug bioavailability was reduced because of dyskeratotic skin, as described in the experimental model by Scholz et al. [4].

The second disease specific treatment prescribed was ivermectin: the efficacy of this drug to cure scabies is close to 100 % after the two doses regimen and it is safe for people weighting ≥ 15 kg and non-pregnant women, being the side effects transient in most cases. Up to 10 doses in subjects experiencing more than one episode/year or who have had more than 3 episodes may be prescribed [1], [5]: there is no specific guideline for ivermectin schedule in the nodular form but the general prescription to treat at least twice with an interval of 7–10 days because the drug had an half-life of 12–56 h and is not ovicidal. Our patient received 17 doses of ivermectin, more than the oral therapy prescribed with a diagnosis of the most severe crusted scabies but in this latter schedule the 10 doses were all assumed in 28 days while our patient took the drug from June 2024 to June 2025.

He showed a significant improvement after the second dose but on the basis of clinical history the treating physician in accord with the patient decided to plan a personalized schedule. The patients had a long-lasting disease with a previous treatment failure to permethrin and, moreover, he was treated twice with topical corticosteroids, aggravating the infestation: furthermore, higher ivermectin doses could be able to overcome a possible resistance to the drug, as shown by the highest response in subjects unresponsive to other treatments treated with two ivermectin doses [6], [ 7].

Tacrolimus ointment was effectively associated with ivermectin therapy: besides the blockade of T-cell activation and therefore, of the elicitation of inflammatory cytokines, maybe its vasoactive properties could help in optimizing ivermectin activity [8]. Of note, this topic treatment can be safely prescribed in immunocompetent patients with on-demand regimen for long [9].

In conclusion, nodular scabies is a rare form of the disease, and it is more frequent in children and that’s why the correct diagnosis can be late in adult patients. The prolonged persistence of skin manifestations can markedly impair quality of life, not only because of the chronicity of genital lesions but also due to the associated anxiety that the infection may remain unresolved. A limit of the report is the lack of photographical material of the lesions at their onset. This case highlights the importance to tailor the clinical approach to a rare clinical manifestation of scabies, mainly if non responder to a first line treatment as was the choice of an innovative, personalized, safe and effective treatment with an ivermectin schedule modeled on the approved one for the crusted form.

CRediT authorship contribution statement

Nicola Bonadiman: Writing – original draft, Conceptualization. Riccardo Rondinone: Writing – original draft, Investigation. Saverio Giuseppe Parisi: Writing – review & editing, Supervision. Monica Basso: Writing – review & editing, Writing – original draft, Supervision, Funding acquisition. Leopoldo Bonadiman: Investigation. Elena Agostini: Writing – original draft.

Consent

Informed consent was obtained from the patient for publication of this case report and any accompanying images.

Ethical approval

Informed consent was obtained from the patient.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.