A 28-year-old female patient was brought to the emergency room with a complaint of dyspnea. She is awake, breathing 34 times per minute with a SpO2 of 93% in ambient air. She has a body temperature of 37.5°C and bilateral diffuse crackles on auscultation. The patient is a PhD student working in the same hospital where she is admitted, with symptoms starting just before leaving the lab to go back home. She regularly spends time in the animal facility as part of her PhD program. She denies allergies and admits to smoking 5 cigarettes per day. The chest x-ray is unremarkable.
What would be the next MOST appropriate next test for this patient?A. Spirometry
Correct Answer: C
Presence of a mild fever and potential occupational exposure to an antigen (triggering respiratory distress) in the absence of wheezing and a negative chest x-ray should point toward hypersensitivity pneumonitis (HP) as an important differential diagnosis. High-resolution CT (HRCT) scan is increasingly used in the initial evaluation of patients suspected with HP. Independently of the disease stage (acute vs subacute vs chronic HP), classic radiologic findings together with a history of appropriate exposure are adequate for establishing diagnosis, and a biopsy can be avoided. CT scan should not be delayed because the classic findings (ground glass opacification in the upper lobes with decreased attenuation of secondary lobules due to air trapping) are best seen during acute presentation and may disappear quickly while symptoms subside. Spirometry may show either a restrictive or an obstructive pattern or both, while diffusion lung carbon monoxide may be impaired in subacute patients and is always impaired in chronic patients. However, these tests are not diagnostic and should not be preferred over a potentially diagnostic HRCT scan. RAST test is useful in determining an IgE-mediated sensitization, which is less likely in this patient especially in the absence of wheezing. ImmunoCAP assay and other techniques to determine IgG-mediated sensitization are useful but may be inconclusive because they lack sensitivity and specificity. Positive findings are not diagnostic for HP and negative findings cannot exclude it. Furthermore, the patient is a smoker, which could yield false positives.