Avaliação da IgG Anti-Péptido Citrulinado Cíclico (CCP) em Doentes Com Artrite Reumatóide, Outras Doenças Difusas do Tecido Conjuntivo e Controlos Saudáveis

Ana Maria Pereira*, Abília Bodas*, Joselina Barbosa†, Miguel Bernardes‡, Luís Delgado§

Serviços de *Imunologia e ‡Reumatologia do Hospital de São João, Porto; †Serviço de Higiene e Epidemiologia e §Serviço e Laboratório de Imunologia da Faculdade de Medicina da Universidade do Porto

 

Resumo

Introdução: A Artrite Reumatóide (AR) é uma doença autoimune sistémica, representando uma das mais graves e potencialmente incapacitantes formas de artrite. Avaliámos neste trabalho a pesquisa e quantificação dos anticorpos IgG para o Péptido Citrulinado Cíclico (IgG anti-CCP), um novo marcador para o diagnóstico da AR, usando um método imunoenzimático. Métodos: A quantificação da IgG anti-CCP foi realizada usando um método imunoenzimático, a da proteína C reactiva (PCR) e factor reumatóide (FR) por imunonefelometria e os anticorpos anti-queratina (AKA) por imunofluorescência indirecta. Estudámos a sensibilidade, a especificidade e o valor predictivo do teste no diagnóstico da AR, comparando--o com o FR e anticorpos AKA. Incluímos 33 doentes com AR, 24 com outras doenças reumáticas (doenças difusas do tecido conjuntivo - DDTC: Lúpus Eritematoso Sistémico n=10, Síndrome de Sjögren n=3, Esclerose Sistémica n=6 e Artrite Indiferenciada n=5) e 30 Controlos. Resultados: Na AR a concentração de IgG anti-CCP foi significativamente superior à das outras doenças reumáticas (mediana 188,7U versus 0,30U p<0,001) e também à dos controlos (1,35U), enquanto que estes dois últimos não diferiram entre si (p=0,573). Encontrámos uma correlação significativa entre o FR e a IgG anti-CCP no total de amostras estudadas (rho=0,698; n=87; p<0,001) bem como na AR. Quando comparámos a AR às outras doenças reumáticas, a sensibilidade e especificidade dos testes diagnósticos foram: IgG anti-CCP 76/83%, FR 76/71% e AKA 48/63%. O valor preditivo positivo para o diagnóstico de AR foi de 0,86 para a IgG anti-CCP, 0,78 para o FR e 0,64 para a AKA. Conclusão: Em doentes com AR a pesquisa de anticorpos IgG anti-CCP por ELISA apresenta uma sensibilidade diagnóstica tão elevada quanto o factor reumatóide, mas com melhor especificidade, afigurando-se como um teste muito útil no diagnóstico diferencial de uma poliartrite.

Palavras-chave: auto-imunidade; artrite reumatóide; IgG anti-CCP; anti-queratina; factor reumatóide; proteína c reactiva; diagnóstico

 

Abstract

IgG Antibodies to Cyclic Citrullinated Peptide (CCP) in Patients with Rheumatoid Arthritis, Other Rheumatic Disorders and Healthy Controls

Background: Rheumatoid arthritis (RA) is a systemic auto-immune disorder and one of the most severe and disabling chronic rheumatic diseases. The objective of this study was to evaluate serum anti-cyclic citrullinated antibodies (anti-CCP) as a new diagnostic tool in RA. Methods: IgG anti-CCP was measured by a second generation enzyme immunoassay, C-reactive protein (CRP) and IgM Rheumatoid Factor (RF) by nephelometry and anti-keratin antibodies (AKA) by indirect immunoflorescence. We evaluated the clinical performance of these tests in terms of sensitivity, specificity, and positive predicted ratio. We studied 57 patients, subsequently classified according to their clinical records in RA (n=33) or other rheumatic disorders (diffuse connective tissue disorders - DCTD: Systemic Lupus Erythematosus n=10, Sjogren Syndrome n=3, Systemic Sclerosis n=6 and Arthropathies n=5) and 30 healthy persons as controls. Results: In RA, IgG anti-CCP levels were significantly higher than in the other rheumatic disorders (median 188.7U versus 0.30U p<0.001) or the healthy controls (1.35U), but did not differ between the two control groups (p=0.573). We found a significant correlation between RF and IgG anti-CCP serum levels in all studied samples (rho=0.698; n=87; p<0.001) and also in the RA subgroup. The sensitivity and specificity of the different tests for RA was: IgG anti-CCP 76/83%, RF 76/71%, AKA 48/63%. The positive predictive ratio for RA diagnosis was IgG anti-CCP 0.86, RF 0.78 and AKA 0.64. Conclusion: In patients with RA the measurement of serum IgG anti-CCP antibodies has a high sensitivity, as seen with IgM RF, but with improved specificity, supporting its usefulness in the differential diagnosis of polyarthritis.

Key-words: autoimmunity; rheumatoid arthritis; IgG anti-CCP; anti-keratin; rheumatoid facto; CRP; diagnosis

 

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Correspondência:

Dr.ª Ana Maria Pereira Serviço de Imunologia Hospital de São João

Alameda Prof. Hernâni Monteiro 4200 - 319 Porto

e-mail: pereira.anamaria@hotmail.com