Abstract
This study investigates the prevalence and clinical and laboratory features of patients with systemic lupus erythematosus (SLE) associated with TB in Chinese patients, as well as its similarities to and differences from patients without TB. Our results show that SLE patients with TB (SLE-TB) might be a subgroup of patients with distinct clinical and laboratory features. Therefore, specific treatment should be given in order to provide a better outcome for SLE-TB patients.
Introduction
Systemic lupus erythematosus (SLE) is a systemic autoimmune disease, characterized by a multitude of autoantibody production, complement activation and immune-complex deposition, causing tissue and organ damage. 1 Major causes of death in patients with SLE include infection, renal failure, central nervous system disease and myocardial infarction. With early meticulous diagnosis and treatment, there has been a significant increase in the survival rate for these patients. 2
Nevertheless, infection still plays an important role in the mortality and morbidity of patients with SLE. 3–6 Although the majority of infections are due to Gram-positive or Gram-negative bacteria, there is increasing evidence indicating that opportunistic infections, such as candidiasis, cryptococcal meningitis and TB, lead to mortality. 2 Previous studies have found that there was an increasing prevalence of TB infection in SLE, especially in endemic areas such as countries in the Far East. 7–9 The high frequency and unusual spectrum of infections can be attributed to the multiple abnormalities of immune function in combination with the effects of immunosuppressive therapy. 2
However, TB in patients with SLE among the Chinese has seldom been studied. Therefore, we investigated the prevalence and clinical characteristics of TB in Chinese SLE patients.
Materials and methods
Patients
We retrospectively reviewed the medical records of 1245 SLE patients who had visited the Department of Rheumatology, Anhui Provincial Hospital and the Department of Rheumatology, First Affiliate Hospital, Anhui Medical University from 1990 to 2001. All the patients fulfilled the 1982 revised American Rheumatism Association criteria for the classification of SLE. 10 The definite diagnosis of TB was confirmed by clinical manifestations and by one of the following: a positive acid-fast bacillus (AFB) smear, a positive culture of Mycobacterium tuberculosis from an appropriate specimen, or a histopathologic finding of caseating granuloma on the specimens.
Demographic data, clinical data and laboratory data were collected from hospital records or by a questionnaire and reviewed by experienced physicians.
Clinical features of SLE patients such as butterfly erythema, photosensitivity, oral ulcer, joint pain, serositis, renal involvement, nervous system involvement, spasm, headache, vasculitis, myositis, skin rash, trichomadesis, serositis, pericarditis and fever were recorded. Renal involvement of SLE was defined according to the American College of Radiology criteria, i.e. any one of the following: persistent proteinuria ≥0.5 g/day; the presence of active cellular casts; or biopsy evidence of lupus nephritis. 10
Major laboratory abnormalities were also recorded, including leukopenia (white blood cell count <4000/mm3), thrombocytopenia (platelet count <100,000/mm3), the occurrence of blood urine or proteuria, the presence of anti-dsDNA antibodies, antinuclear antibodies (ANA), anti-Sm, and serum levels of C3/C4 (by immunoturbidimetry) were also reviewed.
Statistical analyses
The patients were divided into two groups: SLE with TB (SLE-TB) and SLE without TB (SLE-no TB). All data were analysed using SPSS 10.01 software (SPSS Inc, 2000). For comparing the means between different groups, the Student's t-test was used for variables normally distributed data and Mann-Whitney U test for variables not normally distributed. The chi-square test or Fisher's exact test was used to assess differences in prevalence of disease manifestations between the two groups. A probability level of less than 0.05 in a two-tailed test was used as a criterion of significance.
Results
In total, 1245 SLE patients were recruited and 41 (3.3%) of them had TB.
Demographic data
The demographic and general characteristics of the two groups (SLE-TB and SLE-no TB) are summarized in Table 1. Patients with SLE-TB were significantly older than those with SLE-no TB (P = 0.001). In addition, as determined by the time when patients met the 1982 ACR SLE criteria, the onset of SLE was relatively delayed in patients with SLE-TB (P = 0.003).
General feature of the patients with systemic lupus erythematosus patients with TB (SLE-TB) and SLE patients without TB (SLE-no TB)
*P < 0.05; **P < 0.01
†Median (internal of quartiles)
‡Mann-Whitney test
Clinical and laboratory features
The prevalence of distinct disease manifestations and the routine examination of blood and urine in the groups of patients with SLE-TB and SLE-no TB are shown in Table 2. The prevalence of trichomadesis and proteinuria in SLE-TB group was significantly lower than that of SLE-no TB, while the prevalence of serositis was higher in SLE-TB group.
Comparison of disease manifestations between the patients with systemic lupus erythematosus with TB (SLE-TB) and SLE patients without TB (SLE-no TB)
*P < 0.05; **P < 0.01
†Reduction
Discussion
The analysis of our population of 1245 unselected SLE patients revealed the occurrence of TB in 3.3%. This study demonstrates that SLE-TB, in several aspects, constitute a subgroup of patients with SLE. Definitive clinical and laboratory features determine the difference between SLE-TB and SLE-no TB. Our results show that patients with SLE-TB were significantly older with a relatively later-onset of SLE compared with patients with SLE-no TB. In terms of clinical manifestations, there was a significantly lower frequency of renal involvement in patients with SLE-TB than those with SLE-no TB. Therefore, these parameters may be valuable for discriminating SLE-TB patients from SLE-no TB patients.
However, our study has several limitations: the data were collected retrospectively, the potential diagnostic mistakes were unavoidable and the SLE patients in our research were composed of those who were referred to the tertiary hospitals, which may misrepresent the patients who were admitted. Moreover, patients may not have been given the same battery of diagnostic clinical and laboratory tests. Therefore, the ascertainment bias in diagnosis may make the interpretation of the data unclear.
In conclusion, as SLE-TB might be a subgroup of patients with distinct clinical and laboratory features, specific treatment should be taken in order to provide a better outcome for SLE-TB.
Footnotes
Acknowledgements
This work was partly supported by grants from the National Natural Science Foundation of China (30571608, 30771848) and the key programme of National Natural Science Foundation of China (30830089).
J Wang and H-F Pan contributed equally to this work and therefore should both be considered co-first authors.