Abstract
Subcutaneous swellings commonly seen in clinical practice range from benign to malignant. In long standing lesions, fungal abscesses are less commonly suspected. Fine needle aspiration is a first line rapid and reliable method for early diagnosis of fungal infections, allowing prompt and appropriate management.
Introduction
Small subcutaneous swellings are common; they are often diagnosed as epidermoid cysts, cold abscesses, lipomata, or in persistent cases as malignant lesions. However, fungal infections are rarely suspected. Subcutaneous mycoses are caused by fungi present in the natural environment, by direct inoculation of vegetative material through the dermis, usually in rural communities of humid, tropical, or subtropical regions. 1 The understanding of an immune-compromised status, their effect on morbidity and mortality, and the availability of effective anti-fungal drugs have all enhanced the profile of fungi. 2 Fine needle aspiration cytology (FNAC) is the first line investigation for subcutaneous swellings. We highlight some interesting findings to raise awareness of these conditions.
The aim of our study is to analyze the clinicopathological profile of cutaneous fungal infections diagnosed on FNAC. Histopathological examination with special stains such as Periodic acid Schiff stain (PAS), Grocott-Gomori's methenamine silver stain (GMS), wet mount with potassium hydroxide (KOH mount) and fungal cultures help to attain an accurate diagnosis.
Methods
Ours was retrospective observational study conducted at a tertiary care hospital in Central India between January 2023 and December 2024. All who presented with subcutaneous swellings reported as due to fungal aetiology were examined. Demographic data of age distribution, gender, site of involvement, duration of the lesion, total leucocyte count, predisposing factors like thorn injury, other comorbid conditions like diabetes mellitus, chronic non healing ulcers, high blood pressure and malignancy were obtained from online medical records. FNAC was performed using a 23G needle under aseptic precautions. Smears were stained with Haematoxylin and Eosin (HE), Papanicolaou (PAP), May Grunwald Giemsa (MGG), Grocott-Gomori's methenamine silver stain (GMS) and Periodic Acid Schiff (PAS) stains to highlight fungal elements. Subsequent microbiological studies with potassium hydroxide mount and fungal culture were performed. Histopathological follow up and cytological features were correlated whenever possible.
Results
A total of 11 cases of subcutaneous mycosis were detected, (8 male), the age range being 36 to 79 years, in none of whom any inflammatory pathology was suspected. Swellings were most commonly on the upper limb, mainly the forearm, followed by the foot. One patient had a history of previous thorn prick to the leg, one a history of steroid use for two years and one a renal transplantation. Seven were diabetic and nine were pre-diabetic with raised HbA1c levels. Two had a leucocytosis with raised absolute neutrophil count.
All but one showed slender elongated hyphae with septation and acute angle branching (Fig. 1(a)–(c)) morphologically indicative of aspergillus and one a pigmented fungal element. Necrotic background and multinucleated giant cells were also noted with variable amounts of viable and degenerating acute inflammatory cells (Fig. 1(a) and (b)). Granuloma was also seen (Fig. 1(d)). GMS and PAS stain were performed. GMS stain showed black coloured fungal elements in green background (Fig. 2(a) and (b)) Fungal elements are highlighted by bright magenta pink colour on PAS stain (Fig. 2(c) and (d)).
(a) HE, (b) PAP, (c) MGG (40x) – thin branched septate fungal hyphae with giant cell. (d) (HE,40x) – epithelioid cells forming granuloma.
(a) and (b) PAP (40x) – pigmented fungal hyphae, (c) and (d) (PAS,40x) – highlights fungal elements.
On histopathology, five cases were morphologically diagnosed as Aspergillosis, and one showed features of Pheohyphomycosis. Histopathology was not done in other cases (Fig. 3). These findings were confirmed on special stains (Fig. 4).
(a) (HE,10x)– skin with areas of necrosis, (b) (HE,40x)- pigmented fungi, (c) and (d) (PAS,10x;40x) - highlights fungal hyphae.
(a) and (b) (PAS stain 40x), (c) and (d) GMS stain (40x) – highlights fungal elements in histological sections.
KOH mount was performed in five cases; however fungal elements were seen only in one. This suggests that FNAC is more sensitive in detecting fungal elements, and this may be due to a difference in the amount of material studied in both techniques. Multiple smears with different stains are studied with FNAC. However, in the KOH mount only a small amount of the representative sample was examined. This might explain the greater sensitivity of FNAC over KOH.
Fungal culture was performed in three cases, all of whom showed the presence of fungal hyphae with brownish pigment in the cell wall. This pigment was not seen in the smears. This could be most probably due to the presence of only few fungal elements which may have degenerated due to inflammation. However, the culture had abundant fungal elements. Hence the pigment was readily identifiable. This finding highlights the necessity of culture studies after identification of fungal elements on cytology for exact categorization.
The commonest species diagnosed cytologically was Aspergillus in ten and Phaeohyphomycosis in one. Sub-categorization of aspergillus species could not be done.
Discussion
Small subcutaneous mycoses, defined as lesions limited to dermis and subcutaneous tissue eliciting a chronic, localized inflammatory response to fungi, are often overlooked in the absence of severe immuno-compromising disease. 3 These infections occur when fungi invade deeper layers of skin and subcutaneous tissue, typically following trauma or direct inoculation. 4 The relative frequency of types of fungal disease varies geographically (Table 1).
Isolation of different type of fungus in comparison with other studies.
Histopathological examination of the tissue sample is of paramount importance to prove the diagnostic significance of positive fungal cultures as well as the host response to fungus. Most of the fungal profile can be visualized with routine H & E stains but it is difficult to ascertain the genus and species of fungi as their morphological characteristics are not very specific. 2 Special stains help easier identification of the fungal elements. Culture is not always available but molecular testing is useful. 8 Histopathological examination seems more sensitive than conventional microbiological culture.4,7 Cytological evaluation of aspirates is an effective diagnostic tool. The precise identification of a fungal infection is crucial in correct management.
Conclusion
FNAC is a first line rapid and reliable method for the early diagnosis of fungal infections, and is particularly useful where more common diagnoses of small skin lesions are suspected to be wrong.
Footnotes
Acknowledgements
Nil.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
