Adult Black Dot Tinea Capitis Caused by Trichophyton tonsurans Complicated with Herpes Zoster
Tinea capitis (TC) is a common superficial fungal infection of the scalp, with its causative pathogens varying significantly based on geographical location and socioeconomic status. This article presents a detailed case study of a 53-year-old Chinese female who developed TC caused by Trichophyton tonsurans, which was subsequently complicated by herpes zoster. The case highlights the clinical presentation, diagnostic process, treatment regimen, and the potential interplay between fungal infection and viral reactivation.
The patient presented with a three-month history of scalp erythema, scaling, and pruritus. Physical examination revealed erythema, escharosis, and multiple interspersed alopecia patches across the scalp. Dermatoscopy showed scales and corkscrew hairs broken at a distance of 0.5 to 2.0 mm from the scalp, exhibiting a black spot appearance. Direct potassium hydroxide (KOH) examination of scale samples revealed septate hyphae and endothrix spores. Fungal culture on Sabouraud dextrose agar at 25°C yielded colonies that were round with flat edges, white powder on the surface, and brownish-red on the back. Microscopic examination of the colonies revealed branched mycelia, numerous cord shapes, and a small number of pyriform microconidia, some of which expanded into spheres. Macroconidia with transverse septa and thin, curved walls were also observed.
After two weeks of incubation, the colony center became slightly convex, with a surface covered in white villous mycelia and radial furrows. The back of the colony remained flat and reddish-brown. Thick-walled spores were common, and racquet hyphae were occasionally visible. Microculture on potato dextrose agar medium further confirmed the presence of lateral microconidia and abundant thick-walled spores. DNA sequence analysis using internal transcribed spacer (ITS)-1 and ITS-4 primers identified the fungal strain as Trichophyton tonsurans, with a 98.1% consistency to the GenBank accession number AB220045.1.
Antifungal susceptibility testing indicated that the strain was sensitive to both terbinafine and itraconazole. The patient was treated with oral terbinafine (0.25 g/day) and topical naftifine hydrochloride and ketoconazole cream twice daily. After two weeks of treatment, the erythema and alopecia symptoms significantly improved, and subsequent fungal microscopy and culture results were negative.
However, four days after initiating antifungal therapy, the patient developed paroxysmal causalgia in the left head and neck. Clustered tension blisters with a zonal distribution appeared in the painful area, confirming a diagnosis of herpes zoster affecting the maxillary branch of the left trigeminal nerve. Antiviral treatment was administered for one week, resulting in the resolution of scalp erythema and blisters, and the alleviation of neuralgia. Systemic antifungal therapy continued for five weeks, after which the patient fully recovered with only sporadic pigmentation spots remaining. Direct microscopic examination for fungi remained negative.
At the nine-month follow-up, there was no recurrence of TC or herpes zoster. Dermoscopy re-examination showed that the previous lesions were flush and scaled compared to normal scalp areas. Microscopic examination of hair revealed cigarette-ash-shaped proximal hair shafts and white sleeve scales with increased transparency and uneven texture. No scarring or alopecia was observed, and the patient did not experience post-herpetic neuralgia.
TC is typically more common in individuals under 22 years old. However, this case demonstrates that adults can also be affected, particularly in the context of underlying health conditions. The patient had a history of right breast cancer, for which she underwent a radical mastectomy three years prior and was on daily letrozole therapy. Letrozole, an aromatase inhibitor, suppresses tumor growth by reducing estrogen levels. Estrogen plays a crucial role in regulating the immune system, particularly by enhancing macrophage function. A reduction in estrogen levels may therefore compromise immune function, increasing susceptibility to infections such as TC and herpes zoster.
The association between TC and herpes zoster in this case is noteworthy. Herpes zoster results from the reactivation of the varicella-zoster virus (VZV) latent in the dorsal root ganglion. Factors such as infection, trauma, surgery, and immunosuppression can trigger VZV reactivation. In this patient, the skin damage caused by TC may have stimulated the nerve pathways, contributing to the development of herpes zoster in the affected dermatome. This hypothesis aligns with the observation that excessive exogenous stimulation can reactivate latent VZV, leading to herpes zoster in the corresponding dermatome.
The case also provides valuable insights into the changing epidemiology of TC in China. Historically, Trichophyton schoenleinii was the dominant pathogen before 1985, after which there was a shift towards zoophilic fungi, with Microsporum canis becoming the most common causative agent. In Guangdong Province, M. canis, T. mentagrophytes, and T. violaceum were the predominant TC pathogens between 2004 and 2014. T. tonsurans, while common in the United States, Canada, and the United Kingdom, is rare in China, with the last reported case in Guangdong occurring in 2007.
This case underscores the importance of considering rare pathogens in the differential diagnosis of TC, particularly in adults with underlying health conditions. It also highlights the potential for fungal infections to complicate or trigger other conditions, such as herpes zoster, through mechanisms that may involve immune modulation or nerve stimulation. The successful management of this case involved a combination of systemic and topical antifungal therapy, followed by antiviral treatment for herpes zoster, demonstrating the need for a comprehensive and multidisciplinary approach to complex dermatological conditions.
In conclusion, this case of adult black dot tinea capitis caused by Trichophyton tonsurans complicated by herpes zoster provides valuable clinical and epidemiological insights. It emphasizes the importance of thorough diagnostic evaluation, appropriate antifungal and antiviral therapy, and consideration of underlying health conditions in the management of complex dermatological infections. The potential interplay between fungal infections and viral reactivation warrants further investigation to better understand the mechanisms involved and to optimize treatment strategies.
doi.org/10.1097/CM9.0000000000000567
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