title: Clinical utility of LC3 and p62 immunohistochemistry in diagnosis of drug-induced autophagic vacuolar myopathies: a case-control study.
abstract: BACKGROUND
  Some patients treated with chloroquine, hydroxychloroquine, or colchicine develop autophagic vacuolar myopathy, the diagnosis of which currently requires electron microscopy. The goal of the current study was to develop an immunohistochemical diagnostic marker for this pathologic entity.
  
  
  METHODS
  Microtubule-associated protein light chain 3 (LC3) has emerged as a robust marker of autophagosomes. LC3 binds p62/SQSTM1, an adapter protein that is selectively degraded via autophagy. In this study, we evaluated the utility of immunohistochemical stains for LC3 and p62 as diagnostic markers of drug-induced autophagic vacuolar myopathy. The staining was performed on archival muscle biopsy material, with subject assignment to normal control, drug-treated control, and autophagic myopathy groups based on history of drug use and morphologic criteria.
  
  
  RESULTS
  In all drug-treated subjects, but not in normal controls, LC3 and p62 showed punctate staining characteristic of autophagosome buildup. In the autophagic myopathy subjects, puncta were coarser and tended to coalesce into linear structures aligned with the longitudinal axis of the fiber, often in the vicinity of vacuoles. The percentage of LC3- and p62-positive fibers was significantly higher in the autophagic myopathy group compared to either the normal control (p<0.001) or the drug-treated control group (p<0.05). With the diagnostic threshold set between 8% and 15% positive fibers (depending on the desired level of sensitivity and specificity), immunohistochemical staining for either LC3 or p62 could be used to identify subjects with autophagic vacuolar myopathy within the drug-treated subject group (p ≤ 0.001).
  
  
  CONCLUSIONS
  Immunohistochemistry for LC3 and p62 can facilitate tissue-based diagnosis of drug-induced autophagic vacuolar myopathies. By limiting the need for electron microscopy (a time consuming and costly technique with high specificity, but low sensitivity), clinical use of these markers will improve the speed and accuracy of diagnosis, resulting in significantly improved clinical care.
authors.affiliation: Department of Pathology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Han S
authors.initials: HS
authors.lastname: Lee
authors.forename: Brianne H
authors.initials: BH
authors.lastname: Daniels
authors.forename: Eduardo
authors.initials: E
authors.lastname: Salas
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Bollen
authors.forename: Jayanta
authors.initials: J
authors.lastname: Debnath
authors.forename: Marta
authors.initials: M
authors.lastname: Margeta
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry / Q000379:methods*; D016464:Lysosomal Storage Diseases / Q000139:chemically induced* / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008875:Middle Aged; D009135:Muscular Diseases / Q000139:chemically induced* / Q000175:diagnosis* / Q000473:pathology; D000071456:Sequestosome-1 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein