Abstract
Chromoblastomycosis (CBM) is a rare chronic, granulomatous mycosis affecting the skin and subcutaneous tissue. It is a deep, slow growing, fungal infection that most often presents with epidermal changes that clinically appear as a hypertrophic and verrucous plaque. We describe an atypical presentation of an immunocompromised male patient, age 76 years, who presented with a 4-month history of painless subcutaneous firm nodules of the left fifth finger. The fungal culture grew Exophiala bergeri, and histopathology showed medlar bodies with lack of pseuodepitheliomatous hyperplasia or epidermal changes commonly seen in CBM. To our knowledge, this is the first case of Exophiala bergeri CBM in the United States, highlighting its unique clinical presentation and expanding the differentials for a subcutaneous nodule.
- Antifungal therapy
- Chromoblastomycosis
- Exophiala Bergeri
- Neglected fungal infection
- Traumatic inoculation
- sclerotic bodies
- Tropical environment
Chromoblastomycosis (CBM) as a Neglected Tropical Disease (NTD)1 is most prevalent in the humid environment of the tropical and subtropical regions. It is caused by a group of dematiaceous (pigmented) fungi and spores commonly found in soil, wood, and decaying plant matter that penetrate the skin, typically through a minor injury such as a thorn prick or splinter.2-4 The first case of CBM in the United States was reported in Texas in 1933,5,6 and since then, approximately 25 sporadic cases have been reported, particularly in Texas.5 Fonsecaea and Cladophialophora species have been described as the most common causes of CBM and in rare cases, the Exophiala genus.3,4,7,8 The initial lesion typically appears as a small, scaly papule that gradually evolves into larger, warty, nodular lesions characterized on biopsy as hyperkeratotic with pseudoepitheliomatous hyperplasia.8 Diagnosis of CBM relies on both clinical and pathological assessments, which typically reveal “sclerotic bodies” (also known as medlar bodies).3,9 Patients usually require long-term antifungal treatment with itraconazole or terbinafine, with a strong recommendation for excision in small, well-defined lesions.3,7,8.9
Herein, we describe a rare case of Exophiala bergeri CBM with a unique clinical and dermatopathological presentation, acquired endemically in Wisconsin. This case highlights the need for clinicians to widen their scope of differentials for subcutaneous nodules.
Case Report
A male patient, age 76 years, with a history of recurrent follicular lymphoma on cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP)/obinutuzumab, presented with 4-month history of a slowly growing painless mass on the lateral side of his left fifth digit with no associated wound or drainage. The patient did not recall any specific trauma to the finger; however, he reported spending a lot of time cutting wood. Examination revealed a left fifth proximal and middle phalanx subcutaneous firm nodule affecting the volar and dorsal surface (Figure 1). After failing antibiotic treatment, he was referred to an orthopedic surgeon for further evaluation.
Subcutaneous firm nodule affecting the volar and the dorsal surface of the left fifth middle phalanx. Black arrow: Biopsy site.
Radiography of the left hand revealed nonspecific, lobulated swelling around the palmar and ulnar aspect of the fifth finger prompting magnetic resonance imaging, which revealed soft tissue extending along the ulnar and palmar aspect of the proximal and middle phalanges measuring 1.7 × 0.6 × 3.5 cm, and an osseous mass involving the middle phalanx. Overall, the constellation of findings was suspicious for lymphoma, with differential considerations being primary soft tissue sarcoma or possibly hemosiderin-poor tenosynovial giant cell tumor. A skin punch biopsy, revealed a necrotizing granulomatous inflammation with associated pigmented fungal yeast forms consistent with CBM as described in Figures 2, 3, and 4.
Skin punch biopsy with dermal geographic palisading necrotizing granulomatous inflammatory infiltrate (4x, Hematoxylin and Eosin stain).
Numerous pigmented yeast forms (Medlar bodies) within the areas of granulomatous inflammation. Several yeast forms show internal septations (40x, Hematoxylin, and Eosin stain).
The fungal yeast forms are highlighted by a GMS stain (40 x, Grocott-Gomori Methenamine silver stain).
The punch biopsy showed prominent geographic necrotizing granulomatous inflammation diffusely involving the dermis (Figure 2). Significant pseudoepitheliomatous hyperplasia or epidermal changes were not appreciated. The histologic differential diagnosis included infectious necrotizing granulomatous processes and necrobiotic palisading granulomatous dermatitis, including granuloma annulare or a rheumatoid nodule. However, upon higher power examination, numerous pigmented fungal yeast forms (medlar bodies) were present (Figure 3). These appeared as single forms, paired, and in clusters. Occasional internal septations were identified. The overall histologic findings were characteristic of CBM.
The patient was treated with itraconazole 200mg twice daily, and while on this treatment, tissue fungal culture grew Exophiala bergeri on day 49. The patient tolerated this treatment for 8 weeks, but due to concerns for adverse effects of itraconazole, the patient’s immunosuppression and possible need for indefinite treatment referral was granted to the hand surgeon to evaluate for curative amputation. The patient eventually underwent amputation of the left fifth finger 7 months post-initial presentation. The surgical pathology report further confirmed the skin and subcutaneous tissue had florid necrotizing granulomatous inflammation and contained pigmented structures consistent with sclerotic bodies characteristic of CBM. Itraconazole was discontinued 10 days post amputation. Patient follow-up at 6 weeks post amputation showed a well-healed incision with no evidence of complications or recurrence.
Discussion
The global burden of CBM remains unclear. In an article published in 2021, Santos et al.7 estimated the global burden of CBM by retrospectively reviewing publicly available literature from 1914 to 2020 and reported the highest burden in South America (33.8%) and Africa (24.2%), and the least in North America (0.3%),, more so the Northeast and more among immunosuppressed individuals.10 Our patient acknowledged doing a lot of farm work in the woods, so fungal inoculation must have occurred during this time, which is consistent with the mode of transmission described in literature.2-4 Our case is unique, because this patient lives in Wisconsin and reported no history of travel to any countries with a tropical or subtropical humid environment where the fungus has been described to be most prevalent. Our patient’s immunocompromised state and presentation after 4 months of the swelling further illustrated patient characteristics that have been described in previous studies.7,10
Our patient presented with a painless subcutaneous nodule whose differential diagnosis would include, but not be limited to, conditions like subcutaneous granuloma annulare, rheumatoid nodule, subcutaneous sarcoidosis, necrobiosis lipoidica, cutaneous metastases, scleroderma cutaneous tuberculosis, non-tuberculosis mycobacterial infections, among others.11 CBM is a deep fungal infection that usually presents with epidermal changes that clinically appear as hypertrophic and verrucous plaque. A subcutaneous nodule without epidermal changes on histopathology makes our case a unique presentation and expands the differential of a subcutaneous nodule. Additionally, because our patient was an immunocompromised resident of Wisconsin with no history of travel, before the biopsy results, the subcutaneous nodules were suspected to be a neoplastic process, such as lymphoma. Similarly, another subtle case of a 52 year old male was described by Lau et al.12 That patient presented with an 8-year lesion on the tip of the index finger; however, his nodule was tender and smooth, with no pigmentation, which again is not typical of CBM.
The diagnosis of CBM is often confirmed through biopsy staining of the affected tissue, which typically reveals “sclerotic bodies” (also known as medlar bodies), which was seen with our patient. Further description of our patient’s histology revealed the lack of pseudoepitheliomatous hyperplasia or epidermal changes, the main features noted in the stratum corneum and epidermis in CBM,2,13 bringing forth yet another uniqueness here. Moreover, fungal culture grew Exophiala bergeri, which is again another infrequent cause of CBM compared to the most commonly reported Fonsecaea and Cladophialophora species.3,4,7,8 In fact, this is the first Exophiala bergeri caused CBM, to the best of our knowledge.
There are no global guidelines for the treatment of CBM; however, it is essential to remember this is a chronic mycosis, resistant to most treatments and prone to recurrence. Patients depicting all clinical forms pose a significant therapeutic challenge for clinicians, mainly due to the indolent nature and atypical presentation of some cases, as well as diagnostic resource limitations, especially in low to middle-income countries.1,3,4 Long-term antifungal treatment with itraconazole is the recommended standard therapy for CBM, and it is also the most used antifungal drug, with cure rates approximating 80%.3,8 Excisional surgery is strongly recommended for all initial small and well-delineated cutaneous lesions.3,9 Our patient was treated with itraconazole, but given the patient had a solitary lesion, excisional surgery was performed, resulting in a complete cure with no local recurrence.
Conclusion
Chromoblastomycosis should be considered on the differential diagnosis list for patients presenting with a subcutaneous nodule, more so in immunocompromised settings. It is a slowly progressive but notoriously difficult to treat infection with a high risk of recurrence, yet there are no standard treatment guidelines due to the rarity of this disease. Therefore, understanding its etiology, clinical manifestations, and management strategies is vital for healthcare providers, especially in regions where the disease is endemic.
Footnotes
Disclosures: The authors received no financial support for this article’s research, authorship, and publication. The authors have declared no conflicts of interest related to this work.
- Received May 28, 2025.
- Accepted August 12, 2025.
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