Pneumonia associated with a chest-wall abscess is an unusual presentation of Actinobacillus actinomycetemcomitans infection. The slow growth of this common periodontal pathogen creates the setting for underdiagnosis.

Case Presentation
A 48-year-old white alcoholic man presented to the hospital complaining of a swelling in his right axilla of 1-month duration. It had first resolved spontaneously but reappeared 2 weeks before admission. He complained of decreased appetite and a 15-lb weight loss in the past month. He had a cough, which was productive of greenish, blood-streaked sputum for 1 week. He also reported right-sided pleuritic chest pain. He denied fever, chills, or rigor but admitted drinking 6 cans of beer every day; he had last used alcohol a few days earlier.

In addition to alcoholism, his medical history included 50 pack-year cigarette smoking. He was not taking any medications and denied intravenous drug use.

On physical examination, the patient was afebrile and his vital signs were within normal limits. He appeared cachectic and pale and had poor dentition. There were rales in the right upper lung fields. A soft, round swelling was noted under the right axilla that measured 4 to 5 cm in diameter; it was warm and tender to the touch and was not fixed to the underlying structures. The surface and surrounding skin were red; there was no drainage. The remainder of the examination was unremarkable.

Admission laboratory test results included: hemoglobin, 108 g/L; hematocrit, 34.8%; white blood cell count, 15.1 x 10⁹/L, with a left shift; platelets, 1090 x  10⁹/L. Serum chemistries and liver function tests were all within normal limits.

Chest x-ray showed a right upper lobe cavitary infiltrate. A subsequent computed tomography (CT) scan of the chest demonstrated a right apical cavitary lesion, with fluid draining through the parietal pleura into the chest wall (Figure 1), a finding suspicious for pulmonary tuberculosis (TB). The patient was placed in respiratory isolation, and empiric treatment for pulmonary TB was started using a 4-drug regimen.

Bronchoscopy showed that all the segmental and subsegmental airways were normal, except for mucosal friability on the affected side. Purified protein derivative and HIV tests were negative. Three sputum samples were negative for acid-fast bacilli.

Needle aspiration of the axillary mass was performed. Gram’s stain of the purulent fluid showed numerous gram-positive cocci and gram-positive filamentous rods. Acid-fast bacillus stain was negative.

Based on these preliminary results, actinomycosis pneumonia with lung abscess secondary to aspiration was the presumptive diagnosis and anti-TB treatment was stopped. The patient was started on trimethoprim/sulfamethoxazole (TMP/SMX; Bactrim, Septra) and clindamycin (Cleocin) and showed significant improvement. After 7 days of incubation, culture of the axillary fluid grew gram-negative microorganisms, which were initially thought to be a Haemophilus species. The patient was responding to the antibiotic regimen. He started to gain weight, and the swelling in his axilla almost disappeared. He was discharged with a prescription for double-strength TMP/SMX and clindamycin.

After 30 days of incubation, the culture grew A actinomycetemcomitans and Fusobacterium nucleatum. The TMP/SMX regimen was stopped, but clindamycin was continued for a total of 6 months. Repeat CT of the chest after 6 months showed significant improvement, with scarring of the right cavitary lesion and no empyema or subcutaneous axillary abscess collection (Figure 2).

Discussion
A actinomycetemcomitans, a slow-growing, gram-negative bacillus, is a common periodontal pathogen¹ that has been implicated in infective endocarditis.^2,3 It is one of the “HACEK” (Haemophilus aphrophilus, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae) organisms. It occasionally causes soft-tissue infection in association with Actinomyces israelii; hence the name actinomycetemcomitans (“comitans” is Latin for “accompanying”). Soft-tissue infection usually involves the cervicofacial area, but involvement of the chest and abdomen has been documented. Vertebral osteomyelitis, brain abscess, urinary tract infection, and thyroid abscess have also been reported.³ Whether alone or with Actinomyces, it is an important cause of pulmonary infection.⁴ Cases of bronchocutaneous fistula, bronchopleural fistula with subcutaneous abscess, and empyema have been reported.³

Our patient presented with a chest-wall mass secondary to the extension of the infection via the visceral and parietal pleurae. The extension through the soft tissue to the chest wall mimics A israelii or Mycobacterium tuberculosis infection.

Review of the English literature revealed 9 earlier reports of pneumonia secondary to A actinomycetemcomitans. Severe periodontal infection was observed in our case and in 8 of the 9 other cases. In 4 cases and in ours, involvement of the chest wall occurred with either destruction of the rib or a chest-wall mass (Table).^3-6 All 5 patients had pulmonary symptoms for at least 1 month before diagnosis. Nonproductive cough and pleuritic chest pain were presenting features for many of those cases. All patients were afebrile at presentation, and 4 had lost about 5 to 10 lb. Chest x-rays were notable for necrotizing pulmonary infiltrate. CT showed pulmonary and chest-wall destruction, with communication between the chest-wall mass and the pulmonary infiltrate. Bronchoscopy and transbronchial biopsy were performed in 3 cases but did not aid in diagnosis.

In all 5 cases, diagnosis was made either by CT-guided biopsy or by needle aspiration of the chest-wall mass. In our patient, there was concomitant growth of F nucleatum. Since most gram-negative anaerobes respond weakly to Gram’s staining, these organisms can be missed unless the specimen is examined thoroughly, as happened in our case. In 1 other case, Actinomyces grew in addition to A actinomycetemcomitans.⁵ 

In our patient, Gram’s stain did show branching gram-positive bacilli, which were not acid fast. Although Actinomyces failed to grow, it was believed that the branching gram-positive, acid-fast–negative organism was Actinomyces.

Remember that the culture should be kept for more than 1 week, since A actinomycetemcomitans growth is slow and recovery is difficult.⁴ In most reported cases, it took more than 7 days for the organism to grow. All isolates were sensitive to penicillin, but in 2 cases the organism was resistant to clindamycin.^4,5 In all 5 cases, a prolonged course of antimicrobial therapy resulted in cure, without the need for surgical intervention. The duration of antimicrobial therapy varied from 3 months to 1 year.

Because A actinomycetemcomitans is a common periodontal pathogen, infection almost always occurs after aspiration of oropharyngeal secretions. Individuals with depressed levels of consciousness from excessive drug or alcohol use and those with impaired deglutition are at increased risk for developing infection. Good dental hygiene and appropriate interventions to avoid aspiration are important preventive measures.

A actinomycetemcomitans must be included in the differential diagnosis of pneumonia associated with a chest-wall abscess. If a patient with aspiration pneumonia does not respond to clindamycin therapy, consider the possibility that A actinomycetemcomitans is involved. This should, in turn, prompt consideration of proper empiric antibiotic therapy.

Increasingly, penicillin has been replaced by clindamycin as the sole antimicrobial drug for anaerobic bacterial necrotizing pneumonia and abscess.⁵ The high incidence of clindamycin resistance associated with A actinomycetemcomitans can lead to inadequate antibiotic coverage and failed therapy.

Conclusion
A actinomycetemcomitans infection, alone or in combination with Actinomyces species, is an important but unusual cause of pneumonia with chest-wall extension. The chronicity and gradual progression of symptoms, along with chest-wall involvement, can be easily misinterpreted as pulmonary TB, Actinomyces infection, or malignancy. The concomitant presence of A actinomycetemcomitans and Actinomyces in many of the reported cases underscores the importance of saving the culture (for at least 7 days), even when Actinomyces is recovered early. If this relationship is not appreciated, misdiagnosis and mismanagement can ensue.

References
1. Kinane DF, Radvar M. The effect of smoking on mechanical and antimicrobial periodontal therapy. J Periodontol. 1997; 68:467-472.

2. Lockhart PB, Durack DT. Oral microflora as a cause of endocarditis and other distant site infections. Infect Dis Clin North Am. 1999; 13:833-850, vi.

3. Kaplan AH, Weber DJ, Oddone EZ, et al. Infection due to Actinobacillus actinomycetemcomitans: 15 cases and review. Rev Infect Dis. 1989; 11:46-63.

4. Yuan A, Yang PC, Lee LN, et al. Actinobacillus actinomycetemcomitans pneumonia with chest wall involvement and rib destruction. Chest. 1992; 101:1450-1452.

5. Morris JF, Sewell DL. Necrotizing pneumonia caused by mixed infection with Actinobacillus actinomycetemcomitans and Actinomyces israelii: case report and review. Clin Infect Dis. 1994; 18:450-452.

6. Chen AC, Liu CC, Yao WJ, et al. Actinobacillus actinomycetemcomitans pneumonia with chest wall and subphrenic abscess. Scand J Infect Dis. 1995; 27: 289-290.