Mica-associated pulmonary interstitial fibrosis

Our plain-English summary of Mica-associated pulmonary interstitial fibrosis, by S.K. Landas, D.A. Schwartz (The American Review of Respiratory Disease, 1991).

The study

• Authors: S.K. Landas, D.A. Schwartz
• Journal: The American Review of Respiratory Disease
• Published: 1991;144(3 Pt 1):718-21
• Type of article: Case report
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We present the clinical and biopsy findings of a 63-yr-old white male with interstitial pulmonary fibrosis and a long history of extensive exposure to mica while working in the rubber industry. The patient presented 30 yr after the initial exposure with complaints of progressive shortness of breath and a chronic nonproductive cough. Pulmonary function testing revealed restrictive lung function with a mild reduction in the total lung capacity (80% of predicted) and a moderate-to-severe reduction in the diffusing capacity of carbon monoxide (50% of predicted). The chest radiogram and high-resolution chest CT scan showed diffuse fibrosis and focal honeycombing involving the upper and lower lung zones bilaterally. Bronchoalveolar lavage revealed 20% neutrophils in the lavage fluid with abundant rectangular flaking crystals. Open-lung biopsy exhibited extensive fibrosis and architectural remodeling with abundant sheets and fragments of engulfed polarizable crystalline material. Energy-dispersive spectroscopy and electron diffraction studies confirmed the material to have the features of mica. Asbestos and other silicates were not identified. The documentation of prolonged exposure to mica, the clinical and radiographic features of severe interstitial fibrosis, and the histopathologic delineation of the interstitial lesion, including spectroscopic and crystallographic verification of crystalline mica, support the causal relationship between mica and interstitial fibrosis.

In plain English

This case report described one man, a never-smoker, who developed interstitial pulmonary fibrosis (scarring of the lung tissue) and was evaluated at the University of Iowa. From 1946 to 1951 he worked in the core department of a rubber plant, where he shoveled mica into mixers and was exposed to visible clouds of mica dust, along with process oils, carbon black and blowing agents. Later maintenance work added exposure to toluene diisocyanate. Breathing tests showed mildly restricted lung function and reduced gas transfer (65% of predicted). A CT scan showed scarring and honeycombing, more prominent on the right. Lung washings contained 20% neutrophils. An open-lung biopsy showed extensive fibrosis with abundant crystals, which electron analysis matched to mica (muscovite). Asbestos and other silicates were not identified. Steroids did not help, and the patient was placed on oxygen. The authors concluded that this case provided evidence of a causal link between mica and the fibrosis. They acknowledged that the case could be argued to be idiopathic pulmonary fibrosis, and that small amounts of other silicates hidden by the mica remained a theoretical possibility.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report (single patient)
• Who was studied: One 65-year-old white man who had never smoked, a rubber manufacturing worker (1946 to 1986), referred to the Occupational Medicine Clinic at the University of Iowa
• Exposure: Mica dust, process oils, carbon black and 'blowing agents' in the core department (1946 to 1951), including shoveling mica into Banbury mixers amid visible mica dust clouds. Then maintenance work (1951 to 1968) with the same agents plus urethane foam manufacturing, including toluene diisocyanate (TDI).
• Main results:
  • Pulmonary function tests in the patient: TLC 77% of predicted, residual volume 69%, FVC 73%, carbon monoxide diffusing capacity 65% of predicted
  • High-resolution CT showed an interstitial fibrotic process and peripheral honeycombing, more prominent on the right side
  • Bronchoscopy showed increased lavage neutrophils (20%); transbronchial biopsies were nondiagnostic
  • Open-lung biopsy showed extensive interstitial fibrosis and architectural remodeling, with abundant polarizable crystalline material mostly inside histiocytes
  • Electron diffraction data on the crystals matched mica (muscovite)
  • Asbestos and other silicates were not identified; no ferruginous bodies were seen
  • Corticosteroid treatment (60 mg prednisone daily for 3 months) had no effect on symptoms or lung function
  • In March 1990 the patient's oxygen saturation fell from 92 to 80% when walking on level ground, and supplemental oxygen was started
• The authors' conclusion: The authors concluded that the documented prolonged mica exposure, the clinical and radiographic features, and the biopsy findings with spectroscopic and crystallographic confirmation of mica provided evidence in this case for a causal relationship between mica and interstitial pulmonary fibrosis.
• Limitations the authors state:
  • A theoretical possibility remains that small quantities of other fibrogenic silicates, masked by the abundant mica, caused the disease
  • The authors acknowledged one could argue the case is consistent with idiopathic pulmonary fibrosis

Topics

Medical terms in this study, explained in our Lexicon: Mica, Interstitial Fibrosis, Biopsy, Interstitial, Pulmonary Fibrosis, Restrictive Lung Disease, Total Lung Capacity (TLC), Diffusing Capacity (DLCO).

Related studies

• Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province — E. Venter, B. Nyantumbu, et al. (2004)
• Asbestosis: interstitial pulmonary fibrosis and pleural fibrosis in a cohort of asbestos insulation workers: influence of cigarette smoking — R. Lilis, I.J. Selikoff, et al. (1986)
• Inhibition of lung injury, inflammation, and interstitial pulmonary fibrosis by polyethylene glycol-conjugated catalase in a rapid inhalation model of asbestosis — B.T. Mossman, J.P. Marsh, et al. (1990)
• Interstitial pulmonary fibrosis environmental or idiopathic? — G.L. Snider (1985)
• Interstitial pulmonary fibrosis in an automobile body shop worker — A. Fischbein, A.N. Rohl, et al. (1985)
• Relation of spirometric function to radiographic interstitial fibrosis in two large workforces exposed to asbestos: an evaluation of the ILO profusion score — A. Miller, R. Lilis, et al. (1996)

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