Oral Localized Lesion on the Tongue in an Immunocompetent Individual: A Report of a Rare Case With a Comprehensive Review of the Literature

Histoplasmosis (HP) is a sporadic deep fungal disease that rarely shows oral lesions in various clinical forms. It is usually associated with immunocompromised states, but oral HP has also been reported in many immunocompetent individuals. An unusual case of focal oral HP in a 65-year-old immunocompetent male is reported from New Delhi, India (non-endemic region) presenting with oral ulcerative lesions on the floor of the mouth and lateral surface of the tongue. This case report highlights the importance of prompt diagnosis for the success of the treatment of oral HP along with a thorough review of the literature on HP in immunocompetent patients with oral manifestations. The average age of immunocompetent patients with oral HP is 49.65 years with a marked male predilection. The most common intraoral site is the tongue, followed by the gingiva. Also, five intraosseous cases of HP in immunocompetent patients are reported, among which four are seen in patients from Africa and in a much younger age group (mean: 17.25 years).


Introduction
Histoplasmosis (HP) or Darling's disease is a systemic disease caused by a dimorphic fungus, Histoplasma capsulatum, which can lead to various clinical manifestations. It exists in the mycelial form at soil temperatures and changes to the yeast form at normal human body temperatures (37°C) [1,2]. It was first described as encapsulated protozoa by Samuel Taylor Darling, a physician in Panama (1906). This disease is highly endemic in the Mississippi and Ohio River basins in the southern United States. Since then, it has been found in temperate climates worldwide [3]. In Indian literature, Panja and Sen (1954) reported the first case of HP in Calcutta [2]. The mode of infection is the inhalation of dust particles from the soil contaminated with bat or bird feces, containing fungal spores, which are the infectious form of the microorganism. Therefore, the lungs are the main portal of entry for fungal spores. HP can present in three forms, the first being the acute pulmonary form in which the spores reach the small bronchioles or alveoli of the lungs. Secondly, H. capsulatum may take over the earlier diseased part of the lungs, which becomes structurally defective and produces a chronic HP pulmonary form. The third form usually affects the hosts with compromised immunity known as disseminated HP (DH), a unique and possibly fatal form of the disease [4]. Immunosuppressed patients having a history of human immunodeficiency virus (HIV) infection, organ transplantation, long-duration corticosteroid usage, systemic lupus erythematosus, and Hodgkin's lymphoma have been at risk of dissemination of the disease. Fever, weight loss, weakness, hepatosplenomegaly, and mucocutaneous lesions are the most common manifestations of dissemination [5]. More severe and generalized cases can be observed in patients like the elderly or HIV-positive individuals [1]. Oral lesions are rare and usually seen in DH when present [1]. At times, they may present as the early or the only mucocutaneous appearance of the disease [6].
This article presents a rare case of localized oral HP in an immunocompetent Indian male, along with a thorough review of the literature.

Case Presentation
A 65-year-old male patient reported to the outpatient department with a chief complaint of a non-healing painless ulcer on the tongue for four months. The patient had no history of trauma, pain, pus discharge, or paresthesia. No relevant past dental history was present. The patient had a habit of hand-rolled nicotine cigarette smoking 10-12 times a day for 40 years. The patient was a farmer. The patient had no history of coronavirus disease 2019 (COVID-19) and the vaccination for the same. Medical history was noncontributory.
Intraoral examination revealed an irregularly shaped ulcer on the right lateral border of the tongue extending on the ventral surface of the tongue as well as the floor of the mouth measuring approximately 5 x 4 cm in size ( Figure 1). The borders of the ulcer appeared edematous and raised. It was indurated and tender, accompanied by bilateral submandibular lymphadenopathy on palpation. Differential diagnoses of squamous cell carcinoma, traumatic ulcer, and deep fungal infection were considered. An incisional biopsy was carried out for histopathological analysis and routine hematological examinations. All the hematological parameters were within normal limits. The patient tested seronegative for HIV. The patient's fasting and post-prandial blood sugar levels were within normal limits. The fungal culture from the dorsal surface of the tongue showed candidiasis and the ventral surface showed no growth. The biopsy specimen was not sent for fungal culture. Fungal blood and respiratory culture and imaging were not performed, as the patient was not willing to get them done. Chest X-rays were normal. The histopathological analysis revealed numerous ill-defined granulomatous aggregates consisting of epithelioid cells, lymphocytes, and multinucleated giant cells, some of them showing Langhans-type giant cells with central caseation. Multiple round to oval intracytoplasmic inclusion bodies with a peripheral halo were observed. Multinucleated foreign body giant cells were randomly distributed in loosely collagenous connective tissue and moderate infiltration of lymphocytes and plasma cells. Few granulomas were noted between the skeletal muscle fibers and nerves ( Figure 2). Grocott methenamine silver (GMS) and periodic acid-Schiff (PAS) staining showed numerous intracytoplasmic fungal organisms throughout the lesional tissue (Figures 3, 4). Acid-fast bacilli (AFB) staining was negative on the biopsy tissue. A final diagnosis of histoplasmosis was arrived at.

FIGURE 3: Numerous circular yeast-like cells stained black (arrow) scattered throughout the tissue. (A) Grocott methenamine silver (GMS) (40x). (B) GMS (100x, oil immersion) FIGURE 4: Numerous magenta-colored circular yeast-like cells (arrow) scattered throughout the tissue in clusters and individually. (A) Periodic acid-Schiff (PAS) (40x). (B) PAS (100x, oil immersion)
As the patient had only oral involvement, he was treated in the outpatient setting with antifungal drugs. He was given a tablet of itraconazole 200 mg orally thrice daily for three days followed by 200 mg twice daily for 12 weeks. After one month of follow-up, there was a marked resolution of lesions with significant symptomatic improvement ( Figure 5). The patient has been under regular follow-up since then.

Review of the literature
A total of 534 English language articles were retrieved from PubMed using the search words "oral histoplasmosis." Out of these 534 articles, we found 37 articles with only 41 cases of localized oral HP in immunocompetent individuals ( Table 1) [3][4][5]. Our review of the literature suggested that the average age of immunocompetent patients with HP with oral manifestations is 49.65 years ( Table 1). There was a marked male predilection with 31 males and 11 females (2.8:1). The most common intraoral site of localized HP in the cases reviewed was the tongue, followed by the gingiva. Interestingly, of the five intraosseous cases of HP in immunocompetent patients (#2, 8, 11, 12, and 21), four were seen in patients from Africa and in a much younger age group (mean: 17.25 years) compared to the average age of 49.65 years. A possible explanation could be the increased prevalence of Histoplasma duboisii in tropical Africa [18]. H. duboisii differs from H. capsulatum as it manifests commonly as lesions of the skin, subcutaneous tissue, and destructive lesions of bone. Due to their young age and aggressive clinical presentation, most of these destructive lesions were initially suspected to be Burkitt's lymphoma [18].  The mean time between the onset of symptoms and clinical presentation of the oral lesions was found to be 5.65 months (two weeks to four years). The most commonly used diagnostic methods in the reviewed literature were histopathology using hematoxylin and eosin staining, followed by GMS, PAS, and culture. Three out of 42 cases showed negative culture results. Most patients were treated with oral antifungal drugs like itraconazole. Intravenous amphotericin B and surgery were other treatment modalities.

Discussion
Histoplasmosis is predominantly a pulmonary disease, and its ecological reservoir is soil [27]. There are two varieties of H. capsulatum that are pathogenic to humans, H. capsulatum var. capsulatum (endemic in Central and North America) and H. capsulatum var. duboisii (predominant in West Africa), and a third variety, H. capsulatum var. farciminosum, that is an equine pathogen, which exists in Africa [27,42]. This infection is endemic in certain areas of the USA, Brazil, Indonesia, Australia, and Malaysia, with few cases reported from Gangetic plains, Maharashtra, West Bengal, and Uttar Pradesh in India [40]. The fungus spreads by hematogenous route or direct inoculation into the mucosa.
HP is common in immunocompromised patients; however, many studies have shown a high prevalence of DH in immunocompetent patients too, where it tends to be an asymptomatic or self-limited disease, whereas, in immunocompromised patients, it might disseminate in a possibly fatal course of action. Cellmediated immunity is the primary defense mechanism in the human body against the organism leading to granulomatous and histiocytic inflammation in the host [42,43].
The reported prevalence of HP in adults 65 years and older is nearly 3.4 cases per 100,000 population [5]. Its severe form commonly affects infants with known immaturity of immune processes and the elderly because of a decline in cell-mediated immunity [25].
According to Padhye et al. [20], HP in Indians occurs mainly in the extrapulmonary sites, especially in the oral cavity. Localized HP may rarely result from direct inoculation of H. capsulatum into oral mucosa [40]. Oral lesions along with constitutional symptoms like dysphagia, weight loss, loss of appetite, and irregular low-grade fever suggest a clinical differential diagnosis of squamous cell carcinoma, oral involvement of tuberculosis, syphilitic chancre, granulomatosis with polyangiitis, or major aphthous ulcer [23]. A study by De and Nath has shown DH as a critical cause of pyrexia in immunocompetent patients [42]. Most of those affected are from a rural background (85%) and are mainly male, emphasizing the significance of occupation and exposure to the soil as a hint to the diagnosis of DH [42].
The histological differential diagnosis of HP includes other conditions in which parasitized macrophages are seen, like leishmaniasis. Sections of HP show numerous multinucleated giant cells, epithelioid cell granulomas, and mixed inflammatory cells, including multiple histiocytes stuffed with ovoid yeast forms of H. capsulatum, whereas the parasites in leishmaniasis lack the clear halo seen in H. capsulatum and tend to aggregate at the periphery of the macrophage (marquee sign). Leishmania donovani (LD) bodies can be recognized by a nucleus and bar-shaped kinetoplast within each amastigote and are PAS negative [44].
The definitive diagnosis needs isolation of H. capsulatum on special culture media, such as Sabouraud agar, following incubation at 25°C for six to 12 weeks. The fungal colonies appear smooth initially but become cottony, filamentous, and brownish with age. Positive cultures give the most substantial evidence for HP, but most asymptomatic patients have negative cultures. Apart from cultures, skin scrapings, body fluids, and exudates should be analyzed using 10% potassium hydroxide (KOH) and Parker ink or calcofluor white mounts. Tissue sections should be stained using PAS, GMS, or gram stain [45].
Other techniques are also available to supplement a culture and microscopic assessment. Using serology as a marker, antibodies to H. capsulatum can be detected by three available methods: complement fixation (CF), immunodiffusion (ID), and enzyme immunoassay (EIA). An antibody titer of 1:32 or greater on the CF test denotes an acute infection. ID test qualitatively measures precipitating (H and M precipitin bands) antibodies. The H band always specifies active infection, while the M band is less specific. The most sensitive test is EIA but shows a high false-positivity rate. In combination with antigen testing, serology improves the diagnostic yield for acute pulmonary HP though serological testing (antigen and antibody) shows a high rate of cross-reactivity with other fungal species. Serial testing of Histoplasma antigen and antibodies in urine and serum are good ways to assess response to therapy [46]. Polymerase chain reaction diagnosis based on the amplification of fungal gene sequences is an effective tool for detecting invasive mycoses [45].
The treatment depends on the severity of the infection and the patient's medical condition, with antifungal drugs being the treatment of choice [47]. In immunocompromised patients such as those with HIV presenting with limited or disseminated disease, intravenous liposomal amphotericin B is the treatment of choice as the regular (amphotericin B deoxycholate) form is less used due to adverse reactions [48]. However, in immunocompetent patients and those with localized disease, itraconazole is the preferred treatment modality as it is safe and has low toxicity compared to amphotericin [49,50]. The prognosis in immunocompetent patients having mild to moderate infections is usually good. However, the prognosis is poor for patients with severe conditions, those who are immunosuppressed or have chronic cavitary pneumonia, meningitis, or fibrosing mediastinitis.

Conclusions
In conclusion, although localized oral HP in an immunocompetent individual is rare, one must always rule out a hidden immunosuppressive state for optimal treatment outcomes. Also, an HP must be considered in the differential diagnosis of a non-healing oral ulcer despite the absence of pulmonary symptoms. Early diagnosis and management of such a deep fungal disease are crucial to prevent it from getting disseminated throughout the body. On review of the literature, oral HP is most commonly found in elderly males, with the tongue being the most common intraoral site. Such lesions can be frequently mistaken for malignant ulcers, which should always be ruled out before performing any treatment.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.