Actinomycosis & Actinomycetoma
Actinomycosis and actinomycetoma are chronic infections caused by filamentous bacteria. They progress slowly but can cause severe destruction of deep tissues. Although the endings "-mycosis" and "-mycetoma" suggest a fungal disease, the culprits are actually branching, filamentous Gram-positive bacteria (actinomycetes). Actinomycosis is an endogenous infection: the anaerobic/microaerophilic bacillus Actinomyces israelii takes hold when a mucosal barrier is breached. Actinomycetoma, by contrast, is exogenous: aerobic bacteria (Nocardia brasiliensis, Actinomadura madurae, Streptomyces somaliensis) enter directly through open wounds after contact with soil or thorn scratches. Both conditions share a hallmark triad: woody induration, a network of chronic draining sinus tracts that cross anatomic planes, and the discharge of sulfur granules (bacterial grains). At Haute-Derma, our diagnostic workup is comprehensive: direct examination of sinus discharge for grains, Gram and modified Kinyoun staining, skin biopsy to look for the Splendore–Hoeppli phenomenon, and specialized anaerobic/aerobic cultures. We then use prolonged high-dose antibiotic combinations to preserve as much limb function and appearance as possible.
How the disease develops at the cellular and immune level:
- Filamentous Bacteria and Their Route of Entry (Endogenous vs. Exogenous):
- Actinomyces israelii normally lives harmlessly in the mouth, gut, and vagina. When injury, dental work, surgery, or infection tears the mucosa, the bacteria invade the dermis and subcutaneous fat and cause tissue necrosis under anaerobic conditions.
- In actinomycetoma, aerobic actinomycetes living in soil and plants enter through thorn pricks or scratches on the foot (Madura foot). They multiply slowly in the subcutaneous fat and provoke a chronic necrotizing granulomatous reaction.
- Sulfur Granules and the Splendore–Hoeppli Phenomenon:
- In tissue, the branching filaments cluster into tiny spheres 0.5–3 mm across called grains (granules). With Actinomyces, the grains are pale yellow, hence the name sulfur granules.
- The bacteria secrete a glycoprotein matrix around the filament mass, combined with deposits of host IgG and C3 immune complexes and calcium phosphate.
- On histology, the grains are surrounded by the Splendore–Hoeppli phenomenon: a crown of radiating, eosinophilic (pink-red) amorphous material encasing the bacterial cluster. This helps the bacteria resist phagocytosis by neutrophils and blocks the penetration of antibiotics.
- Destruction Across Anatomic Boundaries:
- The bacteria release proteases, collagenase, and hyaluronidase that destroy fat and muscle, forming deep, interconnected cold abscesses.
- Unlike ordinary bacteria, which are held back by fascial planes, Actinomyces can bore through fascia and intermuscular septa and even destroy nearby bone, creating numerous sinus tracts that drain pus onto the skin surface.
Clinical Features
| Form | Characteristic Clinical Features | Pathogenesis and Microbial Burden |
|---|---|---|
| Cervicofacial Actinomycosis (Lumpy Jaw) | A woody, hard plaque at the angle of the jaw, dark red to purple, breaking down into multiple sinuses that drain pus containing yellow grains. | Entry after tooth extraction or oral trauma; anaerobic A. israelii; painless in the early stages. |
| Abdominal/Pelvic Actinomycosis | A stone-hard infiltrated plaque on the abdominal wall or around the navel with chronic draining sinuses; history of an intrauterine device (IUD) or appendectomy. | Spreads from the bowel or uterus to the abdominal skin, destroying the peritoneum and abdominal muscles. |
| Actinomycetoma of the Foot (Actinomycotic Mycetoma / Madura Foot) | A deformed, markedly swollen, painless foot with numerous draining nodules that discharge grains (white, yellow, or red). | Aerobic bacteria (Nocardia, Actinomadura) from soil enter through thorn wounds; destroy the heel and ankle bones. |
| Nodular Draining Actinomycetoma of the Trunk | Raised granulomatous plaques with many sinuses draining mucoid fluid; the surrounding skin is densely fibrotic. | Common in farmers who carry sacks or firewood on their shoulders; enters through friction injuries. |
Actinomycosis vs. Actinomycetoma vs. Eumycetoma (True Fungal Mycetoma)
| Actinomycosis | Actinomycetoma (Bacterial Mycetoma) | Eumycetoma (True Fungal Mycetoma) |
|---|---|---|
| Anaerobic bacterium Actinomyces israelii | Aerobic bacteria (Nocardia, Actinomadura) | True filamentous fungi (Madurella mycetomatis, Scedosporium) |
| Endogenous (mouth, gut) | Exogenous (soil, plants, injury) | Exogenous (soil, arid environments) |
| Soft, pale yellow grains (sulfur granules) | Small grains (<1 mm), white, yellow, or red | Large grains (1–2 mm), usually black or yellow |
| Gram (+), Kinyoun (−) | Gram (+); Nocardia: partially Kinyoun (+) | Gram (−), PAS (+), Grocott (+) (true fungal hyphae) |
| Prolonged penicillin G / amoxicillin | TMP-SMX + amikacin / dapsone | Antifungals (itraconazole / voriconazole) |
Our Approach
At Haute-Derma, we diagnose filamentous bacterial infections according to strict microbiology and pathology standards:
- Grain Collection and Direct Examination (Grain Extraction & Stereomicroscopy):
- Pus is collected by pressing gently around the sinus opening with sterile gauze, or the tract is flushed with sterile saline to collect the grains.
- A grain is placed on a slide with a drop of 10% NaOH or KOH, a coverslip is pressed down gently, and it is examined under the microscope for a mass of interwoven filaments in a radiating sunburst pattern or a cluster of fine filaments.
- Specialized Microbiological Staining Panel:
- Gram stain: Confirms very thin, Gram-positive filaments branching at acute angles, clearly different from true fungal hyphae (>3–5 µm).
- Modified Kinyoun stain (partially acid-fast): Positive for Nocardia spp. (confirming Nocardia actinomycetoma) and negative for Actinomyces israelii.
- Skin Biopsy for Histopathology:
- A punch biopsy or open biopsy that includes the whole wall of the sinus tract and the deep granulation tissue.
- H&E staining shows neutrophilic abscesses around the bacterial grains, the Splendore–Hoeppli phenomenon (a pink eosinophilic rim), and surrounding stroma infiltrated by plasma cells and epithelioid macrophages with dense fibrosis.
- Anaerobic/Aerobic Culture and PCR Identification: Pus or grains are cultured in anaerobic thioglycollate or brain-heart infusion medium at 37°C (if Actinomyces is suspected), or on antibiotic-free Löwenstein–Jensen or Sabouraud medium at 28–30°C (if aerobic actinomycetes are suspected).
Treatment Options at Haute-Derma
Because the grains shield the bacteria and dense fibrosis reduces blood supply, treatment requires prolonged high-dose antibiotics combined with appropriate surgery:
- Treatment of Actinomycosis (Endogenous Actinomyces Infection):
- Intravenous induction phase (2–6 weeks): IV penicillin G (18–24 million units/day, divided every 4 hours) to achieve levels that penetrate the hard fibrotic tissue.
- Oral maintenance phase (6–12 months): Amoxicillin (500 mg by mouth 3–4 times daily) taken continuously until the skin lesions have fully cleared and X-ray/CT shows no remaining infiltrate.
- Penicillin-allergic patients: Doxycycline (100 mg by mouth twice daily), erythromycin, or clindamycin instead.
- Treatment of Bacterial Mycetoma (Actinomycetoma):
- Welch regimen: trimethoprim-sulfamethoxazole (TMP-SMX) (8/40 mg/kg/day by mouth in 2 divided doses) plus amikacin (15 mg/kg/day IV in 2 divided doses for 3 weeks, then 2 weeks off, repeated for 1–3 cycles).
- Alternative regimen: TMP-SMX plus dapsone (100 mg/day) or amoxicillin-clavulanate, continued for 6–12 months.
- Surgical Support and Rehabilitation at Haute-Derma:
- Irrigation and thorough drainage of cold abscesses, and debridement of necrotic sinus tracts.
- Important: Avoid overly wide debridement or amputation early on. Actinomycetoma responds very well to antibiotics; extensive surgery is considered only for severe bone and joint destruction or when medical treatment fails.
