Actinomycosis

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Clinical photograph of the right cervical and submandibular region of an elderly patient, showing multiple suppurative cutaneous lesions. The primary pathology consists of several tender, erythematous nodules and abscesses with central ulceration and spontaneous drainage. A prominent lesion in the lower cervical area exhibits a well-defined, raised inflammatory border surrounding a crateriform defect filled with thick, whitish-yellow purulent material. A second elongated lesion near the jawline shows similar purulent discharge and moisture, suggesting active sinus tract formation. The surrounding skin displays significant erythema and edema, consistent with localized infection. Benign seborrheic keratoses and skin tags are also visible in the periphery. Clinically, these findings represent a case of cervicofacial actinomycosis, characterized by 'lumpy jaw' syndrome with chronic abscesses and draining sinuses that may contain characteristic sulfur granules.

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Actinomycosis

Organism and Microbiology

Actinomyces species are gram-positive, non-acid-fast, anaerobic to microaerophilic, filamentous branching bacteria - not true fungi, despite the name "ray fungus." The most common pathogenic species is A. israelii, followed by A. bovis and A. naeslundii. They are normal commensals found in high concentrations in the tonsillar crypts, carious teeth, colon, and urogenital tract.

Cummings Otolaryngology, p. 1496

Pathogenesis

The organism is non-invasive under normal conditions. Disruption of mucosal barriers (dental trauma, surgery, GI perforation, aspiration) allows tissue invasion, producing a chronic suppurative granulomatous reaction. Key predisposing factors:

Poor oral hygiene / dental disease
Diabetes mellitus
Immunosuppression, long-term steroid use
Malnutrition and alcoholism
Prior GI/abdominal surgery or perforation

Once established, the infection crosses natural tissue planes (fascial, lobar fissures) - a hallmark that distinguishes actinomycosis from other infections.

Classic Forms and Clinical Features

Form	Frequency	Key Features
Cervicofacial	~55%	"Lumpy jaw"; indurated woody mass around mandible/submandibular region; draining sinuses; mandible > maxilla (4:1)
Abdominopelvic	~20%	Often post-appendiceal rupture or surgery; appendix most common site; fistula formation (enteroenteric, enterocutaneous, enterovesical)
Pulmonary/Thoracic	~15%	Infiltrate crossing lobar fissures; pleural involvement >50%; chest wall sinuses; periosteal rib destruction
Primary gastric	Rare	Mimics gastric carcinoma; epigastric mass with fistula/UGI bleed

Cummings Otolaryngology, p. 1496; Sleisenger & Fordtran's GI Disease, p. block12

Cervicofacial - the Prototype

The classic presentation is a painless, indurated ("woody") swelling of the jaw/neck/submandibular region that softens centrally to form multiple draining cutaneous fistulae. Constitutional symptoms (fever, lymphadenopathy) are typically absent. CT shows obliteration of tissue planes and extensive soft tissue destruction.

Cervicofacial actinomycosis - lumpy jaw with multiple draining sinus tracts and purulent discharge

Cervicofacial actinomycosis: multiple suppurative nodules and draining sinus tracts in the submandibular/cervical region. Note the whitish-yellow purulent discharge - characteristic sulfur granules may be visible within.

Pathological Hallmark: Sulfur Granules

"Sulfur granules" are yellow, gritty, 1-2 mm grains visible in pus or discharge. Microscopically they consist of:

Central mass of fine, delicate branching gram-positive filaments
Peripheral eosinophilic clubs (immunoglobulin deposits = Splendore-Hoeppli phenomenon), giving the appearance of "rays" - hence "ray fungus"

They also occur in nocardiosis, but filamentous gram-positive rods in the granule confirm actinomycosis (Nocardia is weakly acid-fast).

Andrews' Diseases of the Skin, p. 316

Diagnosis

Method	Detail
Microscopy	Crushed granule → gram stain shows long gram-positive filaments; most important test
Anaerobic culture	Brain-heart infusion blood agar at 37°C; culture recovery < 50%; takes weeks
Histopathology	Fibrous encasement of multiloculated abscesses with sulfur granules
Fine needle aspiration / fistula swab	Rapid identification of granules
Imaging (CT/MRI)	Mass crossing tissue planes; periosteal proliferation or bone destruction; no respect for anatomical boundaries

The condition is frequently misdiagnosed as malignancy due to the indurated mass appearance - histology is essential.

Treatment

Antibiotics (cornerstone)

First-line: Penicillin G - high doses (10-20 MU/day IV) for 4-6 weeks, then oral penicillin 4-6 g/day for 2-3 more months (total ~3-6 months minimum; some sources say up to 12 months for deep infection)
Actinomyces species have no known resistance to penicillin
Alternatives: Amoxicillin, ampicillin, clindamycin, doxycycline, erythromycin, ceftriaxone, tetracyclines
Gastric actinomycosis: amoxicillin/clavulanic acid for 6-12 months

Surgery

Incision and drainage of abscesses
Excision of devitalized tissue, sinus tracts, and dense fibrotic masses (especially when antibiotic response is poor)
Cure rates approach ~90% despite frequent late diagnosis
Cummings Otolaryngology, p. 1496; Andrews' Diseases of the Skin, p. 316; Sleisenger & Fordtran's, block12

Thoracic Actinomycosis (Pulmonary)

50% have pleural involvement (effusion or marked thickening)
Chest radiograph: localized infiltrate extending across fissures to adjacent lobes + pleural thickening
Chest wall abscess or draining sinus tract is pathognomonic
Bone changes: periosteal proliferation or rib destruction
Pleural fluid: may be frank empyema (PMN-predominant) or serous (lymphocyte-predominant)
Treatment: high-dose penicillin for prolonged periods; pleural effusion managed as any parapneumonic effusion
Murray & Nadel's Respiratory Medicine, block25

Abdominal/Pelvic Actinomycosis

Most common site: appendix (often masquerades as appendiceal abscess)
CT/MRI may show a mass compressing the ileocaecum; sinus and fistula tracts (enteroenteric, enterocolic, enterocutaneous, enterovesical)
Associated with IUD use in women (pelvic actinomycosis)
Grainger & Allison's Diagnostic Radiology, p. block4

Key Differentials

Mimicker	How to distinguish
Malignancy	Actinomycosis crosses tissue planes, has sinus tracts; biopsy/histology decisive
Nocardiosis	Sulfur granules present but organism is weakly acid-fast (Actinomyces is not)
Tuberculosis	AFB positive; caseating granulomas without sulfur granules
Fungal mycetoma	Eumycetoma has larger granules; different organism

Summary Points

Gram-positive anaerobic commensal - NOT a fungus
Disrupted mucosal barriers are the trigger
Crosses tissue planes - hallmark
Sulfur granules + gram-positive filaments = diagnostic
Culture sensitivity < 50%; direct microscopy more reliable
Penicillin is the drug of choice; prolonged therapy (months) is required
Often mistaken for malignancy - biopsy is key
Three main forms: cervicofacial (55%), abdominopelvic (20%), pulmonary (15%)

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