Lobomycosis
Lobomycosis (Jorge Lobo's disease) is a chronic fungal infection of the skin and subcutaneous tissue that progresses extremely slowly. It is caused by Lacazia loboi (formerly named Loboa loboi). Typical lesions are painless, keloid-like nodules, raised bumps or firm warty plaques, found mostly on the ears and the limbs.
It is one of the most unusual fungal infections in the medical literature: Lacazia loboi has never been grown on standard culture media, and it resists most systemic antifungal drugs. At Haute-Derma, we diagnose lobomycosis by its distinctive appearance under the microscope on biopsy, and we plan complete surgical removal with the aim of preserving both appearance and function.
Microbiology and Pathogenesis
An Unculturable Organism With a Bead-Chain Appearance
- Lacazia loboi is a fungus that cannot yet be cultured in the laboratory.
- Appearance in tissue: The fungus is seen as round or lemon-shaped yeast cells with very thick walls, 6–12 µm across. Its hallmark is that the cells are linked by narrow bridges into chains, often described as a "chain of beads" or "string of pearls."
How Infection Occurs and Why Lesions Look Like Keloids
- Risk factors and transmission: The fungus lives in tropical rivers and rainforest environments, and transmission through contact with bottlenose dolphins has been documented. People become infected through minor scrapes, splinters or insect bites.
- Keloid-like fibrous overgrowth: L. loboi triggers a chronic granulomatous reaction while also releasing growth factors that drive fibroblasts to produce large amounts of type I collagen. The result is a firm, smooth, shiny growth, pale pink to violaceous, that closely mimics an overgrown keloid.
Clinical Forms of Lobomycosis
- Keloidal form (the most typical): raised nodules or plaques with a smooth, shiny surface, pink, brown or pale purple in color and firm to the touch, appearing on the ear, face, forearms or lower legs. They look very much like a freely growing keloid and are completely painless, causing at most mild itch or reduced sensation at the site.
- Nodular/verrucous form: bumpy, fissured nodules covered by thick keratin or dry crust, easily mistaken for chromoblastomycosis or squamous cell carcinoma.
- Infiltrative plaque form: well-demarcated, hardened plaques sitting slightly above the surrounding skin and spreading slowly over many years.
- Ulcerative form (rare): usually the result of injury to an existing keloid-like lesion, producing a shallow ulcer that is prone to secondary bacterial infection.
Differential Diagnosis
| Lobomycosis | True keloid | Paracoccidioidomycosis |
|---|---|---|
| Contact with river water or rainforest, minor injury | Prior surgery, acne or old burns | Inhaled fungal spores from soil; mucosal involvement |
| Keloid-like growth on the ear or limbs that never shrinks on its own | Scar that grows beyond the original wound edges | Mulberry-like mucosal ulcers |
| Round yeast cells linked in bead-like chains | Only thick, fibrotic collagen bundles; no fungi | Yeasts with multiple buds ("ship's wheel") |
| Cannot be cultured | No organism | Grows in culture as mold/yeast |
Our Diagnostic Workup at Haute-Derma
Touch Preparation / Direct Microscopy:
- Technique: the lesion surface is lightly scraped or pressed onto a glass slide, and 10%–20% KOH is added.
- Findings: round yeast cells with refractile double walls, joined by thin bridges into straight or branching chains of 3–8 cells.
Skin Biopsy for Histopathology (Essential):
- Epidermis: thinned and atrophic, with loss of the rete ridges.
- Dermis: an intense giant-cell granulomatous reaction, with the dermis packed with Langhans giant cells and epithelioid macrophages.
- PAS and GMS stains: countless Lacazia loboi cells, inside giant cells or lying free in the dermis, arranged in their characteristic bead-like chains.
Immunologic Studies and Ruling Out Other Causes: Because L. loboi cannot be cultured, the diagnosis rests entirely on the chains of fungal cells seen on histology, together with the characteristic clinical picture.
Treatment at Haute-Derma
Wide Surgical Excision: First-Line Treatment
Because Lacazia loboi resists most oral antifungals, complete excision of the lesion with a safety margin of more than 5 mm is the only treatment that offers a good chance of cure.
- Technique: the entire keloid-like mass is removed down to the fascia, or to the cartilage when the ear is involved, and the defect is closed with a local flap or a split-thickness skin graft.
Combined Medical Therapy to Prevent Recurrence
Used for extensive lesions that cannot be fully excised, or after surgery to lower the risk of recurrence:
- Clofazimine: 100 mg/day (or, in combination, 300 mg/month under supervision). Clofazimine accumulates inside macrophages and boosts the innate immune response against the fungus.
- Clofazimine plus itraconazole: clofazimine 100 mg/day with itraconazole 200 mg/day, continued without interruption for 12–24 months.
- Cryotherapy: liquid nitrogen can be used alongside other measures to shrink the keloid-like mass before surgical excision.
