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.

January 7, 2014

Case 1: Histoplasma-associated mediastinal granuloma

1. Infection with Histoplasma can lead to 3 different types of mediastinal involvement: mediastinal lymph nodes, mediastinal granuloma, and fibrosing mediastinitis. This is not a disease spectrum since studies have shown that one does not necessarily lead to the other. 

2. Mediastinal lymph node involvement refers usually to the presence of calcified lymph nodes associated with past infection. 

3. Mediastinal granuloma refers to a more serious condition where active granuloma formation leads to compression of  adjacent structures and sinus tract formation in some cases. 

4. Fibrosing mediastinitis is the most feared complication. For some unknown reason, it usually affects younger females. Its occurrence is most likely predicted not by the burden of Histoplasma infection but by the host's immune response to the fungus. Mediastinal biopsy often reveals only the presence of collagen fibers in contrast to mediastinal granuloma where active caseating granulomas are seen on histopathology.

5. No treatment is recommended for mediastinal lymph nodes or fibrosing mediastinitis. Treatment with itraconazole with or without corticosteroids is considered especially for symptomatic persons with mediastinal granuloma.

Case 2: Refractory and recurrent Pseudomonas bacteremia in an immunocompromised patient (a mortality-morbidity discussion)

1. This highlights the difficulty in managing patients with multidrug resistant Pseudomonas infection.

2.In this case presentation, colistin monotherapy was suggested to be more efficacious compared to aminoglycoside monotherapy in patients with Pseudomonas infection. Please refer to the following studies:

• Leibovici et al. PMID: 9145881. Kuikka et la. PMID: 9865983. Both showed increased mortality with use of aminoglycoside monotherapy against Psudomonas bacteremia.
• Petrosillo, et al. PMID:18844682. Presents data on colistin monotherapy against MDR gram negative organisms including Pseudomonas.

Case 3. A case of severe 2009 H1N1 influenza infection requiring intravenous zanamivir 

1. Intravenous zanamivir is used in patients with either suspected neuraminadase inhibitor resistant strain of influenza or in patients with a perceived impairment in gut absorption of oral oseltamivir.

2. Intravenous zanamivir is generally safe and well-tolerated in phase II studies. Increased AST and ALT may be a concern for some patients receiving this investigation drug.