Solitary Pulmonary Nodule

• definition of a pulm nodule is <3cm diam (anything larger is considered a mass)
• key to approaching a SPN is to risk stratify according to likelihood of cancer
• incidence of cancer in patients with solitary nodules ranges from 10 to 70%
• infectious granulomas cause about 80 % of the benign lesions
• Clinical risk factors for malignant pulm nodule:

· Age (>60= highest risk)

· Smoking status

· History of cancer

· Radiographic findings:

· Size: (<1.5cm=low prob, 1.5-2.2=intermediate, >2.2cm=high)

· Borders: spiculated (corona radiate sign)=high risk, vs. scalloped=intermediate risk vs. smooth=low risk

· Calcifications: suggest benign lesion (laminated/central pattern=granuloma, popcorn pattern=hamartoma)

· Growth rate: volume-doubling time for malignant bronchogenic tumors is rarely less than a month or more than a year

 

Differential Diagnosis:

• Malignant: primary lung Ca, metastatic carcinoma, lymphoma, carcinoid
• Infectious: Mycobacterial granuloma (TB), endemic fungi granuloma (histoplasmosis, coccidioidomycosis), PCP (in HIV + pts), Dirofilariasis (dog heart-worm)
• Benign tumors: hamartomas (benign growth from multiple tissue types)
• Other: AV malformations, bronchogenic cyst, fibroma, intrapulmonary lymph node, sclerosing hemangioma

Diagnostic testing for active pulm TB:

• Gold standard is sputum culture, but this can take up to 2 weeks to grow
• Sputum smear for AFB: sensitivity ~75%, specificity ~95% with 3 serial smears
• False negatives can occur with low organism loads; false positives occur with non-TB mycobacterium
• Nucleic acid amplication (M. Tuberculosis DNA/RNA testing) is being studied, and appears to be more sensitive (with 1 specimen) than 3 repeated AFB smears; the CDC has not yet approved this test, but it likely will be used in the future to improve efficiency, cost effectiveness of TB testing.
• See link to recent study of NAA vs. AFB testing: http://ajrccm.atsjournals.org.laneproxy.stanford.edu/cgi/content/full/178/3/300

Diagnosis of Coccidiodes immitus:

• Routine lab studies are often normal but can include: mild leukocytosis, peripheral eosinophilia, and an elevated ESR
• Remember, cocci is never considered normal flora
• Routine culture is fairly sensitive, usually grows within 1 week; care should be taken by lab personnel b/c spores can be aerosolized from media plates (actually considered a bioterrorism agent).  Not transmissible person-to-person.
• Anti-coccidiodal antibody testing is fairly specific (although not sensitive, as the antibodies may lag acute infection).  Abs can be checked in the serum and other body fluids if indicated (ie. CSF, peritoneal fluid etc.).  There are several commercially available anti-cocci ab tests:

· Immunodiffusion for IgM and IgG (qualitative test)

· Complement fixation: depletion of complement occurs after an infected pt’s antibodies react with a cocci antigen in vitro. Complement depletion is assessed by the failure of “tanned” sheep RBCs to lyse when added to the mixture (normally would be lysed in the presence of complement) (quantitative test--titers can be followed to assess clinical improvement, severity of infection)

· Enzyme-linked immunoassays (EIA) for IgM and IgG—more sensitive than immunodiffusion tests but less specific (qualitative only). Can only be used with a + immunodiffusion test, to confirm

• At Stanford, we send the cocci immunodiffusion and complement fixation tests to the UC Davis Pappagianis lab
• Antibody titers decrease over time, so positive cocci Ab titers are almost always indicative of acute infection (levels decrease to undetectable in pts who clear the infection)

(Victoria Kelly MD, 11/4/10)