A patient who survives the initial exposure to paraquat may later develop pulmonary fibrosis.
Pulmonary exposure may occur as a result of:
(1) a polyamine transport system expressed in the membranes of alveolar cells results in accumulation of paraquat in the lungs.
(2) aspiration
Initially there is an alveolitis which latter progresses to a diffuse fibrosis. In the first week after ingestion a patchy infiltrate is seen in chest X-rays that progresses to ground-glass opacification of the lung fields. Later honeycombing develops.
There is a deterioration in pulmonary function tests prior to worsening hypoxemia.
Paraquat toxicity is dose dependent. Ingestion of less than 20 mg per kg body weight typically does not result in pulmonary fibrosis. Severe pulmonary disease can occur when the ingested dose of paraquat ion is greater than 40 mg per kg body weight.
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