PURPOSE: The utility of evaluation of the lipid content of induced macrophages (lipid macrophage index, LMI) in guiding treatment in patients with asthma or chronic cough (CC) has not been extensively evaluated. It has been suggested to indicate occult aspiration. We evaluated patient characteristics predictive of an elevated LMI in an extended cohort of patients with CC or asthma, hypothesizing if due to microaspiration LMI should be related to BMI and/or rhinosinusitis and a diagnosis of CC. If related to airway cell flux (macrophage ingestion of necrotic/ apoptotic cells) then LMI should be related to total sputum cells.
METHODS: Sputum was induced in 103 adult non-smoking patients with guideline-defined CC or asthma and the percentage of sputum cells positive for lipid inclusions was determined after staining cells with Oil-Red O. Multivariate analyses of 22 demographic and sputum variables were performed using linear regression with covariates selected using Mallow’s CP criterion.
RESULTS: Most patients (86.5 %) had LMI values higher than previously reported norms (norm < 5% positive). This was irrespective of primary diagnosis, with a mean score of 18.1 ± 13.9. 40% of the variation in LMI was explained by measured parameters; multivariate analyses disclosed significant inverse relationships with BMI, exhaled nitric oxide (FeNO) and sputum % eosinophil and macrophage count, as well as positive associations with FEV1 (% predicted),asthma diagnosis, and sputum % lymphocytes. LMI was unrelated to surfactant D levels in induced sputum in a subset of patients, and unrelated to total cell counts or history of rhinosinusitis.
CONCLUSION: An elevated LMI is very common in this population with chronic airway disorders and identifies a patient group with non-eosinophilic airway abnormalities as judged by an inverse relationship with FeNO and % eosinophil count. There was no evidence for an association with GERD as judged by BMI, nor with chronic cough.
CLINICAL IMPLICATIONS: Either microaspiration is common in our clinic population or there are causes other than microaspiration for an elevated LMI; further research should incorporate independent markers of microaspiration.
DISCLOSURE: Robert Kyskan, No Financial Disclosure Information; No Product/Research Disclosure Information