SERUM AND LAVAGE LACTATE-DEHYDROGENASE ISOENZYMES IN PULMONARY ALVEOLAR PROTEINOSIS

Pulmonary alveolar proteinosis (PAP) is a rare disease characterized by the accumulation of lipoproteinaceous material in the alveolar space. Serum lactate dehydrogenase (LDH) has been noted to be elevated in patients with PAP in previous studies. We sought to extend this observation in a series of patients with PAP by looking at total serum LDH concentrations and LDH isoenzyme fractions measured before and after whole lung lavage. Total LDH and LDH isoenzymes were also determined in the lavage effluent. Total serum LDH was elevated before lavage in 10 of 16 patients. Prelavage serum LDH and prelavage alveolar-arterial O2 gradient showed a significant correlation (r = 0.62, p < 0.05). A decrease in serum LDH was found after lavage in all patients in whom postlavage data was available (paired t test, p < 0.01, n = 11), although the magnitude of this decrease varied considerably. The isoenzyme pattern before lavage was isomorphic, and this pattern was unchanged after whole lung lavage. This was in marked contrast to the LDH isoenzyme pattern observed in the lavage effluent, which showed a lower percent LDH1 and LDH2 and a higher percent LDH3, LDH4, and LDH5 when compared with the corresponding prelavage isoenzyme percentages for serum (unpaired t test, p < 0.001). There was no correlation between the total serum LDH concentration and the total lavage LDH concentration. These data confirm that elevated serum LDH is a common finding in PAP. Furthermore, the LDH elevation found consistently in the alveolar fluid points to this as the source of the serum LDH. In addition, this is the first time a sufficient number of patients has been available to statistically demonstrate a decrease in serum LDH levels after treatment with whole lung lavage. The large quantities of LDH found in lavage effluent and the isoenzyme pattern of the lavage LDH suggest that pulmonary cell death occurs in PAP to a considerable extent, but the specific cells that contribute to the lavage LDH and the impact of intraalveolar LDH on serum LDH require further study.