Grade 4 asbestosis does not extend directly from the respiratory bronchiole to the peripheral lung

Our plain-English summary of Grade 4 asbestosis does not extend directly from the respiratory bronchiole to the peripheral lung, by Y. Kawabata, T. Kasai, Y. Kobashi, et al (Histopathology, 2018).

The study

• Authors: Y. Kawabata, T. Kasai, Y. Kobashi, K. Kawahara, T. Uekusa, K. Kurashima, Y. Shimizu
• Journal: Histopathology
• Published: 2018;73(1):29-37
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Aims: To confirm whether or not grade 4 asbestosis progresses from the respiratory bronchiole to the peripheral lung.

Methods And Results: We examined retrospectively the autopsy or lobectomy specimens from 31 cases (29 males; mean age 64 years) satisfying the pathological criteria of grade 4 asbestosis. Asbestos bodies (ABs) were quantified in samples of dissolved lung and in tissue preparations on glass slides. Respiratory bronchiolar lesions were graded as 0, 1 and ≥2. Grade 4 asbestosis was subdivided into an atelectatic induration (AI) and usual interstitial pneumonia pattern (UIP pattern). Five, 10, and 16 cases had grades 0, 1 or ≥2 lesions, respectively, with mean respective numbers of ABs in dissolved lung of 117 000/g dry lung, 468 000/g and 968 000/g; and in specimens on glass slides of seven ABs/cm2 of tissue slice, 34 ABs /cm2 and 195 ABs /cm2 . The differences were significant. Fifteen and 16 cases showed AI and UIP patterns, respectively, with mean respective numbers of ABs in dissolved lung of 1 006 000/g dry lung and 354 000/g, and 186 and 56 ABs/cm2 on glass slides. The differences were significant. AI patterns originated in subpleural lobules or subpleural zonal areas and UIP patterns originated in subpleural, peripheral lobules.

Conclusions: Grade 4 asbestosis does not start in the respiratory bronchiole. The presence of a grade 1 lesion is not required for the diagnosis of grade 4 asbestosis.

© 2018 John Wiley & Sons Ltd.

In plain English

This Japanese study re-examined lung tissue from 31 people (29 men; average age 64) with grade 4 asbestosis, the most advanced, diffuse form of asbestos-related lung scarring. Most were autopsies from the early 1990s, and all met the stricter Helsinki criteria. Of 24 people with a recorded work history, 23 had occupational asbestos exposure. The authors counted asbestos bodies in the lung and graded scarring around small airways called respiratory bronchioles. Five cases had no such airway scarring (grade 0), 10 had grade 1, and 16 had grade 2 or higher. Average asbestos body counts rose significantly across these groups: 117,000, 468,000 and 968,000 per gram of dry lung. Fifteen cases showed a collapse-type pattern called atelectatic induration, and 16 showed a usual interstitial pneumonia pattern. The collapse-type group had significantly higher counts. In both patterns, scarring appeared to begin in the outer parts of the lung, beneath the pleura. The authors concluded that grade 4 asbestosis does not start in the respiratory bronchiole and that a grade 1 lesion is not required to diagnose it. They noted they had no CT scans to follow how the disease developed.

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: Retrospective pathology study of autopsy and lobectomy (lung surgery) specimens
• Who was studied: 31 cases of grade 4 asbestosis meeting the Helsinki criteria, selected from 63 earlier Japanese cases found mainly through annual Japanese autopsy reports, with lung specimens mainly from the early 1990s. The cases were 29 males and 2 females, with a mean age of 64 years (standard deviation 11), and comprised 28 autopsy and 3 lobectomy cases.
• Exposure: Occupational asbestos exposure. Fiber types are not specified. Of 24 cases with a recorded occupational history, 23 had a definite history of various types of occupational asbestos exposure. Among the 21 cases with a recorded duration, the mean was 22 years (standard deviation 10). Exposure was measured in the lung as asbestos bodies per gram of dry lung and per square centimetre of tissue on slides.
• Main results:
  • Of the 31 cases, 5 (16%) had grade 0 respiratory bronchiolar lesions, 10 had grade 1, and 16 had grade 2 or higher.
  • Mean asbestos body counts in dissolved lung were 117,000 per gram of dry lung in the grade 0 group, 468,000 per gram in the grade 1 group, and 968,000 per gram in the grade 2 or higher group. On glass slides the means were 7, 34 and 195 per square centimetre of tissue. The differences were statistically significant for both methods.
  • Across the bronchiolar lesion grade groups, differences in gender, age, and frequency of pleural plaques and pleural adhesions were not statistically significant.
  • Fifteen cases showed the atelectatic induration (AI) pattern and 16 the usual interstitial pneumonia (UIP) pattern. Mean asbestos body counts were 1,006,000 per gram of dry lung in the AI cases and 354,000 per gram in the UIP cases. On glass slides they were 186 and 56 per square centimetre. The differences were statistically significant for both methods.
  • No nonspecific interstitial pneumonia (NSIP) pattern was found among the 31 cases.
  • In AI cases, no preceding anthracofibrotic grade 3 lesions were found in the areas of intraluminal fibrosis. Subpleural lobules (lobules beneath the pleura), mainly panlobular in nature, were considered the main starting points.
  • All 16 UIP-pattern cases showed fibrosis starting in the subpleural, peripheral lobules.
  • Among 26 autopsy cases where the predominantly affected lobe could be identified, 18 were lower-lobe predominant, 3 upper-lobe predominant and 5 diffuse.
• The authors' conclusion: The authors concluded that grade 4 asbestosis does not start in the respiratory bronchiole and that the presence of grade 1 lesions is not required for its diagnosis.
• Limitations the authors state:
  • This was an autopsy study without correlation with high-resolution CT scans, so the authors could not confirm how grade 4 asbestosis developed over time.
  • The authors stated that the study cannot specifically comment on the relationship between asbestos dose and the UIP pattern of fibrosis.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Autopsy, Asbestos Bodies, Interstitial.

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