Paper I — 2025 March (Supplementary (SAY)) (2019 Scheme) — Q9
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Paper I
2025 March (Supplementary (SAY)) (2019 Scheme) · 100 marks · 180 min
Question
A gardner noticed a series of small red ulcerated nodules of 1 cm diameter on the right forearm. She
provides history of having repeated thorn pricks at on the arm. Microscopic examination of biopsy
revealed cigar shaped yeast forms.
(a) What is the most likely causative agent of these lesions 1 mark(s)
(b) Mention the source and risk factor for this infection 1 mark(s)
(c) Add a note on laboratory diagnosis 4 mark(s)
Q96 marksShort Essays
Answer
(a) Most likely causative agent: Sporothrix schenckii — the “cigar-shaped” yeast forms seen on biopsy microscopy is the classical, distinguishing morphological clue for sporotrichosis.
(b) Source and risk factor: Sporothrix schenckii is a dimorphic fungus found as a saprophyte in soil, decaying vegetation, and on plant material (thorns, rose bushes, moss, hay). The classical risk factor is traumatic inoculation through minor skin injury from thorns, splinters, or other plant material — hence its well-known association with gardeners, farmers, and florists (“rose gardener’s disease”), exactly as described in this patient’s history of repeated thorn pricks.
(c) Laboratory diagnosis:
Direct microscopy — biopsy/exudate examined for the characteristic cigar-shaped (elongated, oval) budding yeast forms, though yeast forms may be sparse in tissue, sometimes requiring special stains (PAS, Gomori methenamine silver) to visualize.
Culture — the definitive diagnostic method; grown on Sabouraud dextrose agar at 25–30°C, yielding a mould form with characteristic delicate hyphae bearing conidia arranged in a “rosette/daisy” pattern at the tip of conidiophores; when subcultured at 37°C on enriched media, the organism converts to the yeast form (cigar-shaped budding cells) — demonstration of this temperature-dependent dimorphism confirms the diagnosis.
Histopathology — biopsy shows a mixed granulomatous and suppurative inflammatory reaction; the yeast forms may sometimes be surrounded by an eosinophilic “asteroid body” (a Splendore-Hoeppli phenomenon).
Serology/skin testing — sporotrichin skin test and serological methods exist but are less commonly used than culture, given culture’s high sensitivity/specificity for this organism.
Clinical pattern: typically presents with lymphocutaneous spread — the primary nodule (as in this patient) is followed by a chain of similar nodules progressing proximally along the lymphatic drainage, a distinctive clinical clue supporting the diagnosis alongside laboratory confirmation.
