Rheumatology 2006 45(Supplement 3):iii3-iii4; doi:10.1093/rheumatology/kel282
© The Author 2006. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Epidemiology of connective tissue disorders
M. Gaubitz
Department of Medicine B, Münster University Hospital, Munster, Germany.
Correspondence to: M. Gaubitz, Department of Medicine B, Münster University Hospital, Albert-Schweitzer-Str. 33, D-48149 Münster, Germany. E-mail: gaubitz{at}uni-muenster.de
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Abstract
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The reported prevalence and incidence of connective tissue disorders
are quite variable, depending on differences in study methodology.
Most important differences are the study duration, the classification
criteria used for diagnosis and the country in which the study
was undertaken. Sjögren's syndrome has the highest prevalence
ranging between 0.5 and 3% of a given population. The prevalence
of systemic lupus erythematosus (SLE) is estimated between 15
and 50 per 100 000 individuals, with a female:male ratio of
6–10:1 in the age group between 15 and 40 yrs. The prevalence
of systemic sclerosis is lower, however, varying significantly
between different studies and countries. The prevalence of overlap
syndromes, especially mixed connective tissue disease, is unknown,
and polymyositis and dermatomyositis are regarded as very rare
rheumatic diseases.
Though the classification criteria for the connective tissue disorders have not been developed for the purpose of diagnosing an individual patient, these criteria still are the most valuable tool for the identification of patients with systemic rheumatic diseases such as connective tissue disorders.
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Introduction
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Systemic lupus erythematosus (SLE), systemic sclerosis (SSc),
Sjögren's syndrome (SS), inflammatory muscle diseases and
overlap-syndromes are grouped together as connective-tissue
disorders. Though specific clinical and pathophysiological symptoms
and mechanisms for the different diseases from this group have
been detected, numerous overlapping features (sustained inflammation,
autoimmune processes with the development of specific autoantibodies
and the systemic clinical phenotype involving several organs)
still justify the classification as a group of connective tissue
diseases [
1]. Due to this diversity of clinical symptoms, the
variable course of the disease diagnosis is still challenging
and, as outlined below, epidemiological data difficult to determine.
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Systemic lupus erythematosus
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SLE is a prototypic autoimmune disease with a diverse array
of clinical manifestations. It is one of the most common autoimmune
disorders in women during their childbearing years. Peak incidence
occurs between the age of 15 and 40 yrs, with a female:male
ratio of 6–10:1. Age at onset of disease can range from
infancy to advanced age, however. In pediatric and older-onset
patients, the female:male ratio is
2:1. In the USA, the average
incidence of SLE has been estimated to range between 1.8 and
7.6 cases per 100 000 person-years [
2]. Incidence rates in Europe
are similar, ranging from 3.3 to 4.8 per 100 000 person-years.
The incidence of SLE is greater in Afro-Americans compared with
Caucasians [
3]. SLE shows a much higher frequency among first
degree relatives of patients; it appears in
25–50% of
monozygotic twins.
The prevalence of SLE in the USA ranges from 15 to 50 per 100 000 persons. SLE is diagnosed worldwide with similar incidences as those reported in the USA.
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Sjögren's syndrome
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SS is a slowly progressive, inflammatory autoimmune disease
affecting primarily the exocrine glands. Diagnostic hallmarks
are diminished tear production, xerostomia and presence of autoantibodies,
especially Ro (SS-A) and La (SS-B) antibodies. Differences in
classification criteria (accepting only clinical symptoms of
Sicca syndrome for diagnosis or postulating also serological
parameters of autoimmunity, especially Ro and La-antibodies)
may complicate the interpretation of epidemiologic data.
SS can occur at all ages, but it affects primarily females during the fourth and fifth decades of life. SS frequency appears to increase with age, with a prevalence of about 3% in people above an age of 50 yrs [4]. The female:male ratio is about 9:1.
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Systemic sclerosis
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SSc, also termed scleroderma, is a multisystem disease characterized
by structural and functional abnormalities of small blood vessels,
fibrosis of the skin and internal organs, activation of the
immune system and autoimmunity. The published incidence rates
in the USA [
5] and European countries range between 4.5 and
18.7 new cases per million. The recently reported prevalence
in the USA (260 per million) [
6] appears to be higher than in
other countries (13–48 per million in the UK [
7]; 86 per
million in Australia [
8]. However, another prospective study
from Estonia revealed out a prevalence of around 2280 per million,
perhaps due to a less stringent definition of ‘scleroderma
spectrum disorders’ [
9]. These numbers are so different
from other reports that comparability of inclusion criteria
is doubtful. Overall, there does not appear to be a difference
between countries with cold or warm climates or different regions
within a single country.
Age of onset is most commonly in the range of 30–50 yrs. SSc is uncommon in children younger than 13 yrs. In first degree relatives the prevalence is significantly higher than in the general population: 1.6 vs 0.026% [6]. Like other connective tissue disorders, SSc is also predominant in females with ratios of women to men between 5 and 14:1. Ethnic backgrounds influence survival and disease manifestation. Progressive pulmonary interstitial fibrosis occurs less frequently in Caucasian patients, when compared with Afro-American and Japanese patients. Environmental agents have been implicated in the development of SSc. Silica dust, frank silicosis and exposure to organic solvents, vinyl chloride or L-tryptophan significantly increase the risk of SSc or other fibrosing illnesses.
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Polymyositis and dermatomyositis
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Criteria for the classification of patients with polymyositis
and dermatomyositis include symmetric muscle weakness, evidence
of myositis proven by muscle biopsy, increase in serum skeletal
muscle enzymes, characteristic electromyographic pattern and,
in case of dermatomyositis, typical rash. The overall annual
incidence of polymyositis–dermatomyositis ranges from
2 to 10 new cases per million persons in different populations
[
10]. There is a trend towards increasing incidence in several
communities [
11]. Inflammatory myopathy can occur at any age;
however, there is a bimodal distribution with peaks between
age 10 and 15 yrs in children and between 45 and 60 yrs in adults.
Myositis associated with malignancy and inclusion body myositis
are common after the age of 50 yrs. The female:male ratio is
about 2.5:1; however, inclusion body myositis appears to be
more frequent in men. Inflammatory myositis is most common in
Afro-Americans.
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Overlap syndromes
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Overlap syndromes are defined by a combination of major features
of more than one rheumatic disease present in the same patient
and often defined by a specific serological test. Raynaud's
phenomenon, arthritis and sclerodactyly are common features,
polymyositis and fibrosing alveolitis more serious manifestations.
Due to the diversity of clinical appearance, there exist no reliable estimates addressing the prevalence of overlap syndromes [12]. In general, patients with an overlap syndrome appear to occur less frequent than patients with SLE, but more frequent than patients with SSc or inflammatory myopathy.
Mixed connective tissue disease (MCTD) a special form of overlap syndrome, first described by Sharp, has been subject of debate till today. Many authors do not regard MCTD as a distinctive disease entity; reliable data concerning its prevalence are not available.
The author has received speaker's honorarium for participation at Actelion Winter School 2006.
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References
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- Valter I, Saretok S, Maricq HR. (1997) Prevalence of scleroderma spectrum disorders in the general population of Estonia. Scand J Rheumatol 26:419–25.[ISI][Medline]
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- Oddis CV, Conte CG, Steen VD, et al. (1990) Incidence of polymyositis-dermatomyositis: a 20-year study of hospital diagnosed cases in Allegheny County, PA 1963–1982. J Rheumatol 17:1329–34.[ISI][Medline]
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Abstract
Introduction