Introduction

Although scabies affects more than 200 million people worldwide, nail unit involvement (ungual scabies), particularly in the proximal nail fold, is rare [1,2]. This rarity indicates that ungual scabies is frequently misdiagnosed as nail trauma, nail dystrophy, onychomycosis, or nail psoriasis [3]. Because most ungual scabies are crusted scabies, which are highly infectious, diagnostic delays are particularly hazardous in patients who are immunocompromised and may propagate outbreaks in healthcare facilities [4].

Herein, we present a rare case of ungual scabies in a woman receiving abemaciclib for metastatic breast cancer, emphasizing its implications for infection control and diagnostic vigilance among clinicians, including non-dermatologists.

Case

Ethics statement: This case report was approved by the Institutional Review Board (IRB) of Yeungnam University Hospital (IRB No: YUMC 2025-05-043). Written informed consent was obtained from the patient for the publication of this report including all clinical images.

A 58-year-old Korean woman with a 1-year history of painful periungual swelling and hyperkeratosis involving multiple fingers was referred to our hospital. The patient did not report pruritus. Several courses of topical and oral antibiotics yielded only transient improvements. Her medical history included hormone receptor-positive (HR+) metastatic breast cancer involving the bones and brain. She had been treated with abemaciclib plus letrozole for approximately 2 years, but the therapy had been discontinued 2 months before the current visit. Concurrent medications included prednisolone, dimenhydrinate, levetiracetam, choline alfoscerate, nizatidine, pentoxifylline, tramadol/acetaminophen, rabeprazole, and megestrol acetate oral suspension. The laboratory results showed no hyperbilirubinemia or eosinophilia. The patient’s Eastern Cooperative Oncology Group score was 1. She frequently visited a long-term care facility for supportive care and reported that a recent scabies outbreak had occurred in that facility.

Physical examination revealed erythematous, swollen proximal nail folds with yellowish crusts on the nail plates and nail folds resembling periungual verruca (Fig. 1). Skin biopsy of the proximal nail fold of the right fourth finger was performed because the finger webs, which are common sites for scabies, were spared. Histopathological examination revealed multiple mites within the stratum corneum (Fig. 2), confirming the diagnosis of crusted scabies with ungual involvement.

Although crusted scabies usually requires more intensive therapy than classic scabies, our patient’s condition was clinically limited to the periungual and subungual units without generalized hyperkeratosis, and she was under hospice care. Therefore, we administered ivermectin 200 µg/kg on days 0 and 7 combined with 5% permethrin, applied carefully to the periungual/subungual areas with nail trimming, with a prespecified plan to escalate to a severity-based multidose ivermectin regimen if the response was inadequate. As her caregiver could not bring her to the clinic, follow-up was conducted by telephone, and the patient reported symptomatic improvement. Objective in-clinic reassessment was not feasible and topical permethrin was continued with caregiver assistance.

Discussion

Ungual scabies was first reported in the English literature in 1978 and remains a rare presentation. Including our patient, 33 cases have been reported in the English literature, of which ours is the first to report an association with abemaciclib [2,5].

Abemaciclib is a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) that has shown efficacy in patients with HR+, human epidermal growth factor receptor-2 negative (HER2–) metastatic breast cancer, and HR+, HER2–, node-positive, high-risk early breast cancer when combined with endocrine therapy [6,7]. Common cutaneous adverse effects of CDK4/6i drugs include alopecia, rashes, and pruritus. Although nail and nail bed disorders occur most commonly when combined with other CDK4/6i drugs, including palbociclib and ribociclib, abemaciclib alone can cause nail changes such as onycholysis, subungual hyperkeratosis, and trachyonychia [8].

Abemaciclib can lead to cellular immunodeficiency, impaired B cell function, and susceptibility to crusted scabies, a major form of ungual scabies that is strongly associated with immunosuppression [9,10]. Our patient’s immunocompromised status may underlie the atypical disease manifestations. In our patient, the characteristic finger web involvement was absent, and the lesions were restricted to the periungual folds. Therefore, we hypothesized that the compromised nail unit barrier and immunocompromised status caused by abemaciclib predisposed the patient to ungual scabies. The absence of itching, combined with an immunocompromised status and concurrent use of prednisolone and dimenhydrinate (a first-generation H1-antihistamine) for the symptomatic treatment of brain metastases, could suppress itch perception.

To date, ungual scabies has been described as mimicking nail trauma, nail dystrophy, onychomycosis, and nail psoriasis. However, the present case closely mimicked periungual verruca. Most cases of periungual verrucae are verruca vulgaris and typically exhibit punctate thrombosed capillaries [11], which were absent in our patient. The clinical manifestations of ungual scabies include subungual hyperkeratosis, onycholysis, longitudinal nail splitting, and subungual debris [5]. Dermoscopy can aid in differentiation; however, microscopy or skin biopsy remains the gold standard for excluding other nail diseases. A KOH (potassium hydroxide) mount, which can be performed more easily and simply than a skin biopsy, is generally positive for mites in ungual scabies and fungi in onychomycosis but negative for traumatic nail, nail dystrophy, and nail psoriasis unless there is disease overlap. Routine consideration of scabies in chronic periungual swelling, even in patients with no signs of pruritus, can prevent delays exceeding the mean 10-month interval reported in the literature [2].

Crusted scabies may harbor high mite loads and is generally highly contagious [12]. In a recent outbreak at a Korean tertiary hospital, more than 130 individuals were infected after the admission of a single missed case of crusted scabies [4]. Our patient’s repeated hospital visits while being undiagnosed exemplify this risk. The scabies outbreak at the long-term care hospital to which she was recently admitted may have been the cause of her infestation. Therefore, early diagnosis by non-dermatologists is critical.

No standardized regimen for the treatment of ungual scabies has yet been established. Various agents have been tested, including systemic ivermectin, topical scabicides such as 1% lindane (gamma benzene hexachloride) cream, 10% sulfur ointment, 5% permethrin or phenothrin creams, and keratolytic preparations such as 6% salicylic acid or 40% urea cream applied under occlusion [2]. In several studies, patients with ungual scabies have been treated with oral ivermectin. However, in Korea, oral ivermectin can only be obtained through designated rare-medicine centers, which can hinder prompt treatment.

To the best of our knowledge, this is the first reported case of ungual scabies mimicking periungual verruca in a patient with breast cancer treated with abemaciclib. Although rare, this case suggests that ungual scabies should be suspected in patients with chronic periungual lesions, particularly in patients who are immunocompromised, such as those receiving abemaciclib. Vigilance across clinical departments and awareness of the possibility of scabies among patients who are immunocompromised can curtail hospital transmission and reduce unnecessary costs.

Article information

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

This work was supported by a 2025 Yeungnam University Research Grant (225A580011) from Yeungnam University.

Author contributions

Conceptualization, Data curation, Formal analysis, Funding acquisition, Methodology: MCK, JGK; Investigation, Validation: MCK; Project administration, Resources, Supervision: JGK; Writing-original draft: MCK; Writing-review & editing: MCK, JGK.

Fig. 1.

(A) Hyperkeratotic, verruca-like periungual plaque with paronychia on the right fourth finger, including proximal nail fold and nail plate; the biopsy site is marked in blue. (B) Yellowish scaling confined to the periungual region of the left hand, with sparing of the finger webs.

Fig. 2.

(A) Low-power (scanning) view of the skin biopsy (hematoxylin and eosin [H&E] stain, ×10). (B) Numerous Sarcoptes scabiei mites located within the stratum corneum (H&E stain, ×100).

References

• 1. Thomas C, Coates SJ, Engelman D, Chosidow O, Chang AY. Ectoparasites: scabies. J Am Acad Dermatol 2020;82:533–48.ArticlePubMed
• 2. Gaurav V, Tyagi M, Grover C, Das S. Ungual scabies: a case report and review of literature. Skin Appendage Disord 2024;10:60–8.ArticlePubMedPMCPDF
• 3. Tempark T, Lekwuttikarn R, Chatproedprai S, Wananukul S. Nail scabies: an unusual presentation often overlooked and mistreated. J Trop Pediatr 2017;63:155–9.ArticlePubMed
• 4. Jung J, Kim SK, Kim EO, Choi EJ, Choi J, Chang Z, et al. Management of a large nosocomial outbreak from an index of crusted scabies in a tertiary care hospital, 2023: a retrospective observational study. J Korean Med Sci 2025;40:e7. ArticlePubMedPMCPDF
• 5. Gunawan H, Hidayah RMN, Achdiat PA, Maharani RH, Yulianti F. Nail abnormalities in scabies patients: a systematic review. Clin Cosmet Investig Dermatol 2025;18:1019–32.ArticlePubMedPMCPDF
• 6. Dickler MN, Tolaney SM, Rugo HS, Cortes J, Dieras V, Patt D, et al. MONARCH 1, a phase II study of abemaciclib, a CDK4 and CDK6 inhibitor, as a single agent, in patients with refractory HR+/HER2- metastatic breast cancer. Clin Cancer Res 2017;23:5218–24.ArticlePubMedPMCPDF
• 7. Johnston SRD, Toi M, O’Shaughnessy J, Rastogi P, Campone M, Neven P, et al. Abemaciclib plus endocrine therapy for hormone receptor-positive, HER2-negative, node-positive, high-risk early breast cancer (monarchE): results from a preplanned interim analysis of a randomised, open-label, phase 3 trial. Lancet Oncol 2023;24:77–90.ArticlePubMed
• 8. Alsatti H, AlMalki B, Alghamdi Y. Abemaciclib-associated skin, hair, and nail toxicities: a case report. Cureus 2024;16:e57677. ArticlePubMedPMC
• 9. Ashraf S, Biglow L, Dotson J, Tirona MT. A fatal case of pneumonitis and hypogammaglobulinemia with use of a CDK4/6 inhibitor in metastatic breast cancer: case report. Transl Breast Cancer Res 2022;3:9.ArticlePubMedPMC
• 10. Walton SF, Beroukas D, Roberts-Thomson P, Currie BJ. New insights into disease pathogenesis in crusted (Norwegian) scabies: the skin immune response in crusted scabies. Br J Dermatol 2008;158:1247–55.ArticlePubMed
• 11. Curtis KL, Davis JC, Di Chiacchio N, Di Chiacchio NG, Grover C, Iorizzo M, et al. Diagnosis and management of subungual and periungual verruca: a clinical review. J Am Acad Dermatol 2025;92:861–71.ArticlePubMed
• 12. Cho M, Kim HS. Crusted scabies in a patient with intellectual disability. J Korean Med Sci 2022;37:e151. ArticlePubMedPMCPDF

Figure & Data

References

Citations

Citations to this article as recorded by