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08/05/2011 - CXRs in TB and MRIs in leptomeningeal disease

posted Sep 20, 2011, 7:53 AM by Chief Resident   [ updated Sep 20, 2011, 7:55 AM by Purnema Madahar ]
You successfully made it through the first week on the wards. Well done!
 
The weekends are vulnerable times for our patients, so please pay attention to the hand-offs and coverage. Residents, please make sure that your patients have detailed plans for the weekend, especially if your team is cross-covered. Some specific tips:
 
1. Interns, turn to your sister-team's resident for help when your resident is not in house. You're never alone!
2. If you need help with weekend discharges, page the weekend social worker. Both Saturday and Sunday, a social worker is in house.
3. Detailed instructions on weekend coverage are posted on the white board in the conference room. Please read them! If you find an error or don't understand the instructions, page or call me.
 
In resident report, Jonathan Shuter taught us about tuberculosis in a patient with AIDS. He made some interesting teaching points:
 
1. Appearance of TB on CXR in a patient with AIDS is variable. Since many features of a CXR 'typical' for TB, like cavitary lesions or upper lobe disease, depend on an intact immune system to form granulomas, these are lacking in the immune-compromised host. This observation was confirmed in the attached study on radiographic correlates of TB, done at Columbia. Of interest, the authors found that the classic teaching that primary TB infection presents as lower lobe disease and reactivation TB presents as upper lobe disease might be a myth: in an elegant study using DNA fingerprinting to establish clusters of identical strains as a proxy for recent infection, they found no significant difference in radiographs of primary of reactivation TB.
 
2. If a patient with pulmonary TB coughs in your face, you shouldn't worry: respiratory droplets are too large to reach the alveoli and settle in the pharynx. However, if they don't settle on a surface, these droplets aerosolize and become droplet nuclei 1 to 5 mcm in size that stay airborne and can be inhaled. Therefore, a surgical mask on a patient is sufficient to prevent transmission, as it will stop respiratory droplets and prevent aerosolization. These and other observations about TB control are nicely reviewed in the attached CID paper co-authored by Gary Kalkut, now Chief Medical Officer at Montefiore.
 
In CRS, Jerry Paccione took us on a journey of clinical reasoning. Ashwin Sridaran was inspired to find a paper that provides some probs to the case discussed:
 
Q: What is the sensitivity of MRI with gadolinium in the detection of leptomeningeal metastasis, established in a population with known metastatic cancer?
A: sensitivity 76%, specificity 77%
 
Due to a lack of a gold standard (CSF cytology only has a sensitivity of about 75% in the detection of leptomeningeal mets), the authors of the attached paper use complicated statistical method to determine the test characteristics of MRI. Maybe one of our clinical epi gurus can weigh in on the validity of these findings?

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