INTRODUCTION: Legionella micdadei or “Pittsburgh pneumonia agent (PPA)” (1) is a rarely isolated organism that accounts for over 60% of infection caused by non-pneumophilia Legionella species. Initially identified as the etiologic agent in an outbreak of pneumonia at the Pittsburgh VA in the early 1980s, it has since been described to cause severe pulmonary infection both in the immune deficient and normal host. We report a case of asymptomatic pulmonary nodules caused by Legionella micdadei in a patient with newly diagnosed CNS lymphoma on corticosteroid therapy.
CASE PRESENTATION: A 64-year-old woman presented to an outside hospital with confusion. Brain imaging revealed a basal ganglia lesion and stereotactic brain biopsy confirmed primary CNS lymphoma. She was started on intravenous dexamethasone (4 mg every 6 hours) and transferred to our institution ten days later. The pulmonary service was consulted for an abnormal CT chest. She denied any respiratory complaints. Past medical history: rheumatic fever in childhood. Social history: former smoker (5 pack years); no history of intravenous drug use. She denied exposure to tuberculosis; PPD status was unknown. She had no recent travel, animal or toxin exposure. Physical examination was unremarkable. CT scan of the chest done on admission to our institution to evaluate extent of disease revealed multiple bilateral pulmonary nodules that were new compared to a chest CT done two weeks earlier. Lab data: WBC count 25.5; LDH 407. Blood cultures and fungal serologies including aspergillus galactomannan and beta-D-glucan were negative. Urine legionella antigen was negative. A 2D-ECHO showed moderate aortic stenosis; no vegetations visualized. CT-guided needle biopsy of one lung nodule was non-diagnostic. Despite a one week course of empiric levofloxacin, a repeat chest CT showed increase in the size of nodules. Bronchoscopy with bronchoalveolar lavage (BAL) and VATS wedge lung biopsy of left upper and lower lobes nodules was done. BAL cultures were negative. Pathology of the lung biopsies revealed an inflammatory infiltrate with micro-abscesses and areas of organizing pneumonia, and no evidence of malignancy. Stains for microorganisms (Gram, AFB, GMS and Fite) were negative. Culture of biopsy material grew gram-negative rods that were further identified as Legionella micdadei. The patient was treated with a 3-week course of levofloxacin with subsequent radiographic improvement of the lung nodules, and is currently receiving treatment for CNS lymphoma.
DISCUSSIONS: Legionella micdadei is a rarely isolated gram-negative rod that is often weakly acid-fast in fresh specimens. In an initial case series of 26 patients (1), 88% were hospital-acquired infections, 50% of patients were immunocompromised for various reasons and 46% had an underlying malignancy. A majority (>85%) were symptomatic with fever and cough. While Legionella micdadei typically causes lobar or segmental infiltrates, varied radiologic presentations have been described, including pleural effusions and cavitary pneumonia. Pathology shows a neutrophilic alveolitis, microabscesses, and macrophages with intracytoplasmic bacilli. Organizing pneumonia within areas of fibrotic nodules has also been described (2).
CONCLUSION: This is a unique case of asymptomatic pulmonary nodules caused by Legionella micdadei in a patient immunocompromised by steroid use and underlying malignancy. Since Legionella micdadei is a rarely isolated organism, a high index of suspicion is needed to make the diagnosis. Legionella micdadei pneumonia should be considered in the differential diagnosis of causes of multiple pulmonary nodules.
DISCLOSURE: Hala Moukhachen, No Financial Disclosure Information; No Product/Research Disclosure Information