Differentials
Abdominal abscess
SIGNS / SYMPTOMS
Features of sepsis or an acute abdomen are generally prominent, although the early symptoms of abdominal actinomycosis may be similar to an abdominal abscess.
INVESTIGATIONS
Histology and culture for actinomycetes are negative.
Blood or site cultures identify etiologic organism.
Ovarian or oviductal tumor
SIGNS / SYMPTOMS
Symptoms may be similar to pelvic actinomycosis. However, the association of a pelvic mass in an IUD user strongly suggests the diagnosis of actinomycosis. Leukorrhea is less likely to be present.
INVESTIGATIONS
Histopathology shows malignancy. Histology and culture for actinomycetes are negative.
Appendicitis
SIGNS / SYMPTOMS
Features of an acute abdomen are generally prominent, but symptoms may be otherwise similar to abdominal actinomycosis.
INVESTIGATIONS
Histology and culture for actinomycetes are negative.
Blastomycosis
SIGNS / SYMPTOMS
Lung blastomycosis may spread to the skin, but otherwise symptoms may be similar to pulmonary actinomycosis.
INVESTIGATIONS
Sputum smear and culture using KOH preparations or specific stains can confirm diagnosis. Histology and culture for actinomycetes are negative.
Brain abscess
SIGNS / SYMPTOMS
Clinical features may be similar to actinomycosis of the CNS.
INVESTIGATIONS
Blood cultures may be positive with a bacterial abscess. Histology and culture for actinomycetes are negative.
Colon cancer
SIGNS / SYMPTOMS
Clinical features of abdominal actinomycosis may mimic colon cancer.
INVESTIGATIONS
Histology shows malignant tissue. Histology and culture for actinomycetes are negative.
Gastric adenocarcinoma
SIGNS / SYMPTOMS
Symptoms of abdominal actinomycosis may mimic gastric adenocarcinoma.
INVESTIGATIONS
Histology shows malignant tissue. Histology and culture for actinomycetes are negative.
Crohn disease
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Colonoscopy shows skip lesions. Biopsy shows characteristic changes. Histology and culture for actinomycetes are negative.
Ulcerative colitis
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Biopsies show continuous distal disease with characteristic changes and an absence of granulomata. Histology and culture for actinomycetes are negative.
Diverticulitis
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Colonoscopy or sigmoidoscopy may show diverticula. Histology and culture for actinomycetes are negative.
Liver abscess
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Blood cultures may be positive in pyrogenic liver abscess. Histology and culture on aspirated fluid is negative for actinomycetes. Ultrasound demonstrates a variably echoic lesion.
Lung abscess
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from thoracic actinomycosis.
INVESTIGATIONS
Very high WBC count is common. Sputum Gram stain and culture may reveal a causative pathogen. Histology and culture for actinomycetes are negative.
Lung cancer
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from thoracic actinomycosis.
INVESTIGATIONS
Sputum cytology may reveal malignant cells. Biopsy shows malignant cells. Histology and culture for actinomycetes are negative.
Nocardiosis
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Modified acid-fast staining of biopsy tissue or other samples allows distinction between Nocardia and Actinomyces.
Pelvic inflammatory disease
SIGNS / SYMPTOMS
History of recent sexual contact, recent onset of menses, or a sexually transmitted infection in the partner, as well as a past history of PID, are common. However, the clinical symptoms of PID may resemble pelvic actinomycosis, and definitive diagnosis requires laparoscopy with biopsy sampling followed by histology.
INVESTIGATIONS
Culture of vaginal secretions may be positive for a sexually transmitted organism. Endometrial biopsy may show changes of endometritis. Histology and culture for actinomycetes are negative.
Pneumonia (fungal, bacterial, or aspiration)
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from thoracic actinomycosis.
INVESTIGATIONS
Sputum Gram stain and culture may reveal a causative pathogen. Histology and culture for actinomycetes are negative.
CXR may typically show focal changes in bacterial pneumonia, with large pleural effusion, cavitating changes indicating an abscess, or multifocal or interstitial changes.
Pulmonary tuberculosis
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from thoracic actinomycosis.
INVESTIGATIONS
Sputum smear and culture positive for acid-fast bacilli. Tuberculin skin testing is usually positive. Histology and culture for actinomycetes are negative.
Intestinal tuberculosis
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from abdominal actinomycosis.
INVESTIGATIONS
Histology and culture of infected tissue positive for acid-fast bacilli. Tuberculin skin testing is usually positive. Histology and culture for actinomycetes are negative.
Uterine cancer
SIGNS / SYMPTOMS
Clinical features may be indistinguishable from pelvic actinomycosis.
INVESTIGATIONS
Biopsy tissue at laparoscopy shows malignant tissue. Histology and culture for actinomycetes are negative.
Whipple disease
SIGNS / SYMPTOMS
Typically presents as an acute GI illness, with fever, diarrhea, and weight loss, often with features of malabsorption such as steatorrhea, edema, fatigue, and lethargy. A severe wasting syndrome with abdominal lymphadenopathy and abdominal pain may develop. Joint problems often occur, and a seronegative migratory arthralgia of the large joints or other forms of arthritis may be the presenting feature. Most patients are anemic.
INVESTIGATIONS
Anti-Tropheryma whipplei-positive macrophages, carried out on biopsied tissue, are a diagnostic marker. Polymerase chain reaction testing of duodenal biopsies positive for T whipplei (although carriers may also have positive results).
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