Certainly! Apologies for the previous omissions. Below is the complete LaTeX document that includes all the requested sections, arguments, code snippets, and proofs, organized logically into a single cohesive document. “‘latex Diagnosis and Treatment of Foot Fusarium Infection Confirmed by Next-Generation Sequencing Technology: A Case Report and Literature ReviewKey Clinical MessageThis case highlights a rare cutaneous Fusarium solani infection in an elderly patient with chronic foot ulcers, initially misdiagnosed due to nonspecific manifestations. Traditional fungal cultures were negative, but diagnosis was confirmed via 18S rDNA and ITS sequencing. Targeted itraconazole therapy based on antifungal susceptibility led to significant clinical improvement, emphasizing the critical role of molecular diagnostics and tailored antifungal treatment in managing such infections.AbstractFusarium spp. are opportunistic fungal pathogens, with an increasing incidence of infection observed in immunocompromised populations. Due to the non-specific clinical manifestations of cutaneous Fusarium infections, they are often misdiagnosed or overlooked. This article reports a case of an 84-year-old male patient with a chronic foot ulcer, diagnosed as Fusarium solani species complex (FSSC) infection through histopathological examination, fungal culture, 18S rDNA sequencing, and Internal Transcribed Spacer (ITS) sequencing of the fungal ribosomal gene region. The patient’s condition improved following individualized antifungal therapy. Combined with a literature review, we discuss the clinical characteristics, diagnostic and therapeutic strategies, and treatment challenges associated with FSSC skin infections. This case underscores the diagnostic limitations of traditional fungal culture methods and highlights the need for improved diagnostic approaches, including 18S rDNA sequencing, and Internal Transcribed Spacer (ITS) sequencing, to ensure early and accurate diagnosis.Treatment should be guided by antifungal susceptibility testing and host immune status, with particular attention paid to antifungal resistance in Fusarium species.Keywords: Fusarium spp.; Cutaneous Fusarium infection; Fusarium solani; 18S rDNA sequencing; ITS sequencingIntroduction Fusarium species are saprophytic fungi and emerging opportunistic pathogens in humans[1],with cutaneous infections posing significant diagnostic challenges. Their clinical manifestations are highly nonspecific, often mimicking bacterial cellulitis or other hyalohyphomycoses[2], leading to frequent misdiagnosis and delayed intervention. Conventional diagnostic methods, including histopathology and fungal culture, are hampered by low sensitivity and inability to achieve species-level identification. This is critically important as members of the Fusarium solani species complex (FSSC), the most prevalent clinical group, exhibit variable and often intrinsic antifungal resistance[3]. We herein present a case of a refractory foot ulcer in an elderly patient, where the etiology was definitively identified as FSSC only through the application of 18S rDNA and Internal Transcribed Spacer (ITS) sequencing. This case highlights the indispensable role of molecular diagnostic techniques in confirming invasive fusariosis and facilitating targeted antifungal therapy, thereby improving patient outcomes.Case History/examination2.1Case History：An 84-year-old male farmer was admitted to the hospital due to ”skin lesions on the foot for over 3 months, aggravated for 1 month.” The patient developed painless nodular rashes on the sole and arch of the foot following a skin injury more than 3 months prior. The rash later spread to the dorsum of the foot, but no special treatment was sought. One month before admission, the lesions further expanded, accompanied by progressive swelling and significant pain while walking. The patient visited a local clinic and received topical medication (details unknown) with poor efficacy. No significant medical history was reported. Physical examination revealed stable general condition, with no obvious abnormalities in systemic examination. On dermatological examination, there was significant swelling over the left dorsal foot. An approximately 8 x 6 cm, dark red, honeycomb-patterned infiltrated plaque was observed. The plaque was non-tender to palpation with mildly elevated local skin temperature.The lesions on the sole were milder than those on the dorsum. No obvious ulceration was observed, but dark brown, viscous purulent discharge was noted upon squeezing the plaque.(Figure 1)2.2 Examinations2.2.1 Laboratory TestsPre-admission blood tests: Neutrophils 76%, lymphocytes 14.9%, eosinophils 0.1%, absolute lymphocyte count 1.06×10⁹/L, absolute monocyte count 0.61×10⁹/L, C-reactive protein (CRP): 6.45 mg/L.Post-admission biochemical, coagulation, blood culture, GM test, PPD test, immunology panel, and tumor markers showed no significant abnormalities. CRP: 15.46 mg/L, 17.5 mg/L. G test: 122.155 pg/mL.2.2.2 Fungal and Bacterial ExaminationsFungal cultures obtained from skin scrapings on two separate occasions revealed no microbial growth. In contrast, fungal culture of a punch biopsy specimen confirmed the presence of a fungal infection (Figure 2). Antifungal susceptibility testing demonstrated susceptibility to amphotericin B, voriconazole, and isavuconazole, with resistance to posaconazole, flucytosine, and fluconazole. Two consecutive bacterial cultures of cutaneous exudate revealed polymicrobial growth comprising ≥3 distinct species.2.2.3 HistopathologyA biopsy from the medial dorsum of the left foot revealed subcutaneous granulation tissue with old hemorrhage and microabscess formation. Periodic acid-Schiff (PAS) and methenamine silver staining showed no definitive fungal elements, consistent with inflammatory changes.(Figure 3)2.2.4 18S rDNA and ITS SequencingFungal colonies from the biopsy tissue were subjected to genetic identification. PCR-amplified fragments were compared with sequences in the GenBank nucleotide database using the Illumina MiSeq platform. 18S rDNA sequencing identified Fusarium sp., showing 99.58% similarity with strain MN602643.1. ITS sequencing identified Fusarium solani species complex, with 100% similarity to strains MK409996.1 and DQ452447.1. Molecular biology confirmed the pathogen as belonging to the Fusarium solani species complex.(Figures 4)3 Diagnosis and TreatmentThe patient was diagnosed with ”cutaneous Fusarium infection” through histopathology, fungal culture, 18S rDNA, and ITS sequencing. Initially, empirical treatment with ceftriaxone (2g IV once daily) was administered, combined with alternating wet compresses of Compound Huangbai Liquid and 3% boric acid solution, along with red-blue light phototherapy. After 7 days, the skin lesions showed no significant improvement. Following pathogen identification as Fusarium via fungal culture and molecular biology, the treatment was adjusted to itraconazole capsules (0.1g orally twice daily) and compound glycyrrhizin tablets (50mg orally three times daily), alongside topical application of butenafine hydrochloride cream and compound salicylic acid-benzoic acid ointment (alternated twice daily). After 2 weeks of targeted therapy, the left foot edema significantly subsided, the lesion area reduced by approximately 60%, pain resolved completely, and inflammatory markers normalized. The patient was discharged with outpatient follow-up after a negative repeat fungal microscopy.A telephone follow-up 2 weeks post-discharge revealed further reduction in foot rash and swelling, with no new lesions reported.4.Literature Review4.1 Clinical Characteristics Analysis （Table 1）Through searches using the keywords ”Fusarium solani” in databases including CNKI, Wanfang, and PubMed, we collected complete case reports of cutaneous Fusarium solani species complex infections from 2003 to 2024. A total of 16 Chinese and 38 English articles were included, comprising 58 cases (including the present case; see Table S1). The literature types included retrospective analyses and case reports. Among the patients, 33 were male and 25 were female, with ages ranging from 3 to 92 years (mean age: 41.37 years). Twenty-one patients had no underlying diseases, while 37 had underlying diseases, including hematologic malignancies (21 cases), diabetes (7 cases), post-transplant status (2 kidney transplants + 1 liver transplant), trauma from traffic accidents (2 cases), burns (2 cases), thyroid disorders (1 case), chronic kidney disease (1 case), and Behçet’s disease (1 case). Twenty-two patients were receiving immunosuppressive therapy at admission, including chemotherapy (17 cases) and corticosteroid treatment (5 cases). Three patients had received antifungal prophylaxis (itraconazole in 2 cases, posaconazole in 1 case) prior to the Fusarium solani species complex infection.Twenty-three patients underwent microscopic examination or culture of skin lesion secretions, while 39 underwent histopathological biopsy and culture of skin tissue. Twenty-two patients also underwent molecular biological diagnosis. Antifungal susceptibility testing was performed in 25 cases, revealing sensitivity to amphotericin B (14 cases) and resistance (2 cases), sensitivity to voriconazole (8 cases) and resistance (4 cases), and sensitivity to terbinafine (4 cases) and resistance (2 cases).4.2 Treatment and OutcomesForty-three patients were cured, 10 died, and 5 discontinued treatment or were lost to follow-up. Thirty-one patients received monotherapy (itraconazole in 11 cases; amphotericin B in 9; voriconazole in 7; terbinafine in 2; luliconazole in 1; efinaconazole in 1). Twelve patients received combination therapy with amphotericin B and voriconazole, while one patient received amphotericin B combined with voriconazole and posaconazole, and another received amphotericin B combined with voriconazole and terbinafine.5 DiscussionFusarium is widely distributed in the environment and primarily acts as a plant pathogen.Human cutaneous infections caused by Fusarium are relatively rare [1]. Such infections predominantly occur in immunocompromised individuals, particularly those with neutropenia or long-term corticosteroid use[4]. Notably, in immunodeficient or immunocompromised patients, approximately 50% of cutaneous Fusarium infections may progress to disseminated disease, clinically manifesting as persistent neutropenia accompanied by multiple papules, nodules, and necrotic lesions[5]. The uniqueness of this case lies in the fact that, although the patient had no typical history of immunodeficiency, age-related immune decline may have been a key factor contributing to the persistent infection.Diagnosing cutaneous Fusarium infections is challenging due to their nonspecific clinical presentation, which can mimic bacterial infections or tuberculous ulcers[6]. A comprehensive evaluation based on clinical assessment, laboratory tests, fungal culture, and molecular methods is required for diagnosis[7]. Culture and direct microscopy of skin biopsy specimens remain the most common diagnostic methods for Fusarium infections, but traditional culture methods have low positivity rates and difficulties in species identification[1]. In this case, initial scrapings were culture-negative, and bacterial cultures of local secretions twice revealed mixed bacterial flora, necessitating further molecular testing for definitive diagnosis. Combining tissue biopsy culture with molecular detection significantly improves diagnostic accuracy[8].The GenBank/EMBL/DDBJ databases contain numerous ITS sequences of Fusarium species, enabling species identification through rDNA ITS sequencing. In this case, sequencing of 18S rDNA and ITS from cultured biopsy specimens using the Illumina MiSeq platform confirmed the diagnosis as Fusarium solani species complex infection. The Fusarium solani species complex comprises at least 26 distinct phylogenetic species, which are morphologically similar but may exhibit varying antifungal susceptibility profiles. Molecular methods such as ITS sequencing can typically identify the pathogen to the complex level, but further multilocus sequence typing (MLST) is often required for species-level identification within the complex [9]. In this case, despite the use of PCR and sequencing, resolution was achieved only to the complex level, which is consistent with the limitations of ITS sequencing for discriminating among closely related species within the FSSC. This limitation underscores the importance of acknowledging the complex nature of Fusarium taxonomy and the potential implications for antifungal therapy, as susceptibility may vary among species within the complex.This multimodal diagnostic approach not only overcomes the limitations of traditional morphological identification[9] but also provides critical guidance for precise treatment, compensating for the shortcomings of conventional methods[10].Due to Fusarium’s inherent resistance patterns, treatment is often challenging. Early diagnosis and prompt initiation of effective antifungal therapy are crucial for successful outcomes. Studies indicate that susceptibility to antifungals varies among Fusarium species, necessitating the use of at least one active antifungal agent, often in combination (e.g., liposomal amphotericin B with voriconazole)[5]. Given the potential for disseminated infection, comprehensive management—including surgical debridement, removal of infected foreign bodies, and optimization of immune status—is essential. In this case, the patient improved after targeted itraconazole therapy (0.1g twice daily) based on susceptibility results, demonstrating that even in non-classical hosts, early precision diagnosis and tailored antifungal treatment can yield favorable outcomes. For clinically suspected cases, timely tissue sampling for multimodal testing is critical, along with routine antifungal susceptibility testing and individualized treatment plans.Cutaneous Fusarium infections are rare and diagnostically challenging due to their diverse presentations. This case highlights the importance of establishing a standardized ”early recognition–precise diagnosis–targeted treatment” workflow to improve outcomes. Particularly in aging populations, heightened vigilance for atypical infections in elderly patients iswarranted.