Validity of internal expression of the major histocompatibility complex class I in the diagnosis of inflammatory myopathies
- Roberta Salaroli1,
- Elisa Baldin2,
- Valentina Papa1,
- Rita Rinaldi3,
- Lucia Tarantino1,
- Lucilla Badiali De Giorgi4,
- Marco Fusconi5,
- Nazzarena Malavolta4,
- Riccardo Meliconi6,
- Roberto D'Alessandro2,
- Giovanna Cenacchi1
- 1Dipartimento Clinico di Scienze Radiologiche e Istocitopatologiche, Alma Mater Studiorum, Università di Bologna, Bologna, Italy
- 2Dipartimento di Scienze Neurologiche, Alma Mater Studiorum, Università di Bologna, Bologna, Italy
- 3Dipartimento di Medicina Interna, dell'Invecchiamento e Malattie Nefrologiche, Azienda Ospedaliero-Universitaria di Bologna, S Orsola-Malpighi, Bologna, Italy
- 4Dipartimento di Ematologia, Oncologia e Medicina di Laboratorio, Azienda Ospedaliero-Universitaria di Bologna, S Orsola-Malpighi, Bologna, Italy
- 5Dipartimento Malattie dell'Apparato Digerente e Medicina Interna, Azienda Ospedaliero-Universitaria di Bologna, Policlinico S Orsola-Malpighi, Bologna, Italy
- 6Dipartimento di Medicina Clinica, Alma Mater Studiorum, Università di Bologna, Bologna, Italy
- Correspondence to Professor Giovanna Cenacchi, Dipartimento Clinico di Scienze Radiologiche e Istocitopatologiche, Alma Mater Studiorum, Università di Bologna, Via Massarenti, 9, Bologna 40138, Italy;
- Accepted 5 August 2011
- Published Online First 10 November 2011
Objective The inflammatory myopathies (IMs) are a group of disorders characterised by weakness and inflammation of the skeletal muscles. Muscle biopsy is the most crucial test to confirm the clinical diagnosis, but also the most common cause of misdiagnosis. There are currently no markers specific or sensitive enough to distinguish IMs from other diseases with similar clinical and morphological features, and an international multidisciplinary effort is under way to develop new classification criteria for IMs.
Methods Standards for Reporting of Diagnostic Accuracy recommendations to validate a diagnostic test based on the quantification of internal major histocompatibility complex class I (MHC-I) positive fibres were adopted. MHC-I immunostained specimens from 64 patients were scored by two independent blinded investigators, and the percentage of positive fibres was determined. Agreement between investigators was evaluated with the k-weighted statistic. The receiver operating characteristic curve, area under the curve, sensitivity, specificity, and positive and negative predictive values of each percentage range of positive fibres versus the diagnosis of IM were calculated.
Results The main difference between IM and non-inflammatory samples was the number of internal MHC-I positive fibres. The k-weighted value was 0.89 for a percentage of MHC-I positive fibres above 50%; the positive predictive value was 100%, and the negative predictive value was 94%.
Conclusions This is the first study on the validity of a quantitative analysis of internal MHC-I positive fibres for an IM diagnosis performed according to Standards for Reporting of Diagnostic Accuracy recommendations. The interobserver agreement was almost perfect, thus making the method reproducible. Applying an MHC-I cut-off above 50% is an optimal marker for polymyositis (PM) and dermatomyositis (DM) diagnosis.
- Inflammatory myopathies
- major histocompatibility complex class I (MHC-I)
- Bohan and Peter's criteria
- STARD recommendations
- electron microscopy
- autoimmune laboratory investigations
- rheumatological pathology
- filament proteins
Competing interests None.
Ethics approval The biopsies were performed according to usual clinical practice for diagnostic purposes. (“S.Orsola-Malpighi Ethical Committee”)
Provenance and peer review Not commissioned; externally peer reviewed.