RESPIRATORY COMPLICATIONS IN MIXED CONNECTIVE TISSUE DISEASE - 09/09/11
Résumé |
The term mixed connective tissue disease (MCTD) was coined by Sharp and coworkers in 1972 to distinguish the patients with combined clinical features of systemic lupus erythematosus (SLE), scleroderma or progressive systemic sclerosis (PSS), and polymyositis–dermatomyositis (PM–DM).62 Previously, clinicians have used various terminologies to describe the clinical disease in patients who demonstrate clinical features of more than one rheumatologic disease. The descriptive terms have included overlap syndrome, undifferentiated connective tissue disease, sclerodermatomyositis, rheumatoid arthritis and systemic lupus erythematosus (RUPUS), systemic lupus erythematosus and progressive systemic sclerosis or scleroderma (lupoderma), or mixed collagenosis.7, 19 Even though the concept of MCTD as a distinct clinical entity has been questioned, an international symposium on MCTD determined that, “on the basis of clinical, serologic, and immunologic data, MCTD seems to be a distinct entity.”3 Based on HLA type to predict differentiation of MCTD, some investigators have suggested that MCTD is, for most patients, an intermediate stage in a genetically determined progression to a recognized connective tissue disease, and those whose disease remains undifferentiated might be considered a distinct subset.17 Furthermore, long-term follow-up of patients with the documented diagnosis of MCTD has shown that most patients with anti-(U1)snRNP antibodies have or will develop a classified connective tissue disease (SLE, PSS, or rheumatoid arthritis [RA]) within 5 years after clinical presentation.68 Other investigators have concluded that antibodies to RNAsmall nuclear ribonucleoprotein (snRNP) do not identify a particular subgroup within the overlap syndromes and that MCTD does not seem to be a distinct entity.38 These observations question the concept of MCTD being a distinct clinical entity.
A prerequisite for the diagnosis of MCTD is the presence of high titers of autoantibodies against uridinerich snRNP Ag.62 Sera containing snRNP are usually present in patients with MCTD, but are uncommon in patients with SLE, PSS, PM–DM, RA, or other rheumatologic diseases. The Sm antibodies and high titers of antinative DNA, detected in SLE, are uncommon in MCTD. In patients with MCTD, serum complement levels are usually normal or only slightly reduced and rheumatoid factor is present in more than half the patients.63 The characteristic laboratory abnormalities in MCTD include high titer (>1:1000) of speckled antinuclear antibodies (ANA), high levels of antibody to RNAse sensitive extractable nuclear antigen (ENA), and presence of snRNP antibody.63 The opinion that the presence of high titer of antibody to ENA and the absence of antibodies to Sm antigen are specific for MCTD has been debated.2 Furthermore, many patients who initially exhibit the specific ENA can become anti-snRNP and others originally diagnosed as having MCTD may subsequently demonstrate more classical clinical features of PSS or SLE.14
It is equally important to note that other prospective long-term studies of patients with MCTD have supported the concept of MCTD as a distinct entity.42 It has been suggested that the concept of MCTD as a distinct disease entity is better replaced by the term undifferentiated autoimmune rheumatic/connective tissue disorder because many of these patients later convert into PSS or SLE, and some remain undifferentiated.9 A review of the literature indicates that many investigators in the field now consider MCTD a distinct entity.1, 10, 13, 27, 40, 41, 52, 53, 56, 59 The various classification criteria suggested for the diagnosis of MCTD are shown in Table 1
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| Address reprint requests to Udaya B. S. Prakash, MD, Pulmonary, Critical Care, and Internal Medicine, East-18, Mayo Building, Mayo Medical Center, Rochester, MN 55905 |
Vol 19 - N° 4
P. 733-746 - décembre 1998 Retour au numéro
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