January 14, 2013 Grand Rounds

Case 1: Chronic cavitary pneumonia  secondary to Pseudomonas aeruginosa

1. This case is particularly interesting as Pseudomonas aeruginosa usually presents as acute pneumonia. Acute necrotizing pneumonia with cavitary formation is a well-recognized complication of Pseudomonas pneumonia. But chronic and progressive cavitary pneumonia secondary to Pseudomonas aeruginosa is probably rare. Although, chronic Pseudomonas airway infection is common among cystic fibrosis patients.

2. Burkholderia pseudomallei, the causative agent of meliodosis, was brought up as a differential diagnosis since the patient is a veteran. Like Mycobacterium tuberculosis, it can lie dormant and reactivate ("Vietnamese time bomb"). As much as 12% of infected patients present with tuberucolosis-like illness, many of whom have cavitary lesions in the upper lobes of the lungs.

Case 2: Necrotizing fasciitis secondary to Klebsiella pneumoniae

1. There are 2 main types of necrotizing fasciitis (NF).

• Type 1 NF: caused by mixed aerobic/anaerobic bacteria; there is usually an obvious portal of entry; you can see gas on radiographic imaging; hard to distinguish from gas gangrene secondary to Clostridium perfringens and Clostridium septicum.
• Type 2 NF: caused by group A Streptococcus, other beta-hemolytic Streptococcus and Staphylococcus aureus; usually no obvious portal of entry; rare to see gas on radiographic imaging.

2. In the western hemisphere, Klebsiella is the 3rd most common causative agent of NF, at least in 1 case series. In Asian countries, on the other hand, it usually is the most common cause, again at least in 1 case series. This may not be so surprising as the hypermucovisous strain of Klebsiella (its most aggressive phenotype) is also more common in Asian countries. The latter is known to cause severe disease including bacteremia, liver abscess, and meningitis.

Case 3: Primary cutaneous aspergillosis

1. Majority of cutaneous aspergillosis represent dissemination from distant foci of infection. A rare disease, primary cutaneous aspergillosis usually results from local trauma to the skin (e.g. intravenous catheter, burn) in immunosuppressed patients.

2. Primary cutaneous aspergillosis is associated with less signs of systemic toxicity compared with primary cutaneous zygomycosis.

3. Voriconazole +/- surgical debridement is the treatment of choice.