Transcript Document

Comorbidity in SLE Compared with Rheumatoid Arthritis and Non-inflammatory Disorders
Frederick
1National
1
Wolfe , Kaleb
1,2
Michaud ,
Tracy
3
Li ,
Robert S.
4
Katz
2University
Data Bank for Rheumatic Diseases, Wichita, KS;
of Nebraska Medical Center, Omaha, NE;
3Bristol-Myers Squibb, Princeton, NJ; 4Rush University Medical Center, Chicago, IL
Abstract
Purpose: Although comorbidity is well described in SLE, there have been no
head-to-head comparisons of comorbidity prevalence in SLE and other rheumatic
conditions. We used self-report comorbidity from patients participating in a
longitudinal study of rheumatic disease outcomes to evaluate comparative
comorbidity and the potential contribution of fibromyalgia; to describe the
prevalence of comorbid condition in SLE,; to determine the relative risk (RR) of
comorbidity in SLE compared with other rheumatic conditions; and to evaluate
the effect of FM.
Methods: We evaluated 1,316 community SLE patients, 14,252 with rheumatoid
arthritis (RA), and 3,768 with non-inflammatory rheumatic disorders (NIRD),
excluding FM, and a comorbidity index was calculated (Michaud 2007). The
presence of FM was determined using survey FM criteria (Katz 2006). We
determined damage by the newly developed Lupus Damage Index Questionnaire
(LDIQ), a self-report version of the ACR/Systemic Lupus International
Collaborating Clinics (SLICC) Damage Index (SDI).
Results: The comorbidity index score was significantly increased in SLE 2.6 (95%
CI 2.5, 2.7) compared with RA 1.7 (1.7, 1.7) and NIRD 1.9 (1.8, 1.9), and this
increase was observed at all age levels and remained significant after non-linear
adjustment for age and sex. To test the potential effect of simultaneous
fibromyalgia, we examined differences between the comorbidity index before and
after adjusting for the presence of FM using survey FM criteria. The presence of
FM was associated with a 1-unit increase in the comorbidity index, but did not
change the comorbidity scores in the 3 disorders. Survey FM was present in
24.4% with SLE, 17.0% with RA and 14.4% with NIRD. Hypertension (37.4%)
and depression (33.8%) were the most common current comorbid conditions
among those with SLE. SLE patients differed most from those with RA in RR of
current comorbid renal disease (RR 5.7), neurologic disorder (3.7), myocardial
infarction (RR 2.8), pulmonary disease (RR 2.3), and stroke (RR 2.0). Patterns
were very similar when SLE was compared with NIRD, and in comparisons
utilizing lifetime rather than current comorbidity. Comorbidities in SLE, as
measured by the comorbidity index, were most strongly associated with the LDIQ
damage score (r=.502) and with SF-36 PCS (r=.383), SF-36 pain (r=.359), and
with the Symptom Intensity Scale (FM scale) (r=.331). Associations with
correlation coefficients <0.300 included fatigue, patient global, SF-36 mental
health, and HAQ disability.
Conclusion: Comorbidity is increased generally in SLE compared with RA and
NIRD, including expected cardiovascular and renal conditions. Although more
patients with SLE satisfied survey FM criteria, the presence of FM did not alter
the increase in comorbidity in SLE. Increase in comorbid conditions is consistent
with known increased mortality in SLE.
References: Michaud, K. Best Prac Clin Rheum 21:85-06; Katz, R. Arth Rheum
54:2006, 169-76.
Table 1. Lifetime comorbidity in
Fibromyalgia, SLE, RA, and Noninflammatory rheumatic disorders (NIRD).
Results
Prevalence of lifetime comorbidity. Table 1 in columns 2 and 5, displays the
prevalence of comorbid conditions adjusted to the estimated age and sex
distribution of the 2004 US population. Columns 1 and 4 show the crude
(unadjusted) prevalence, and asterisks indicate the level of the odds ratio (OR) for
the crude prevalence after adjustment to the mean age and sex in the overall cohort.
Figure 1. The relation of age to comorbidity score. RA and
NIRD scores increase with age, but FM and SLE score are
generally constant for ages 35 through 84.
Considering crude and adjusted percentages in RA, the highest prevalence of
lifetime comorbidity (see table 1) was found for hypertension (47.5%), any GI
problem (42.4%), any psychiatric problem (36.0%), depression (34.4%), GU
problems (30.3%), endocrine problems (30.3%), and cataract (27.0%). The percent
of patients with current problems is, expectedly, much less. The most common
problems in RA are hypertension (32.5%), any endocrine problem (20.3%), any
psychiatric problem (15.9%), any GI problem (15.4%), depression (15.5%), cataract
(9.7%), and diabetes (9.1%).
Comparative comorbidity. We used logistic regression to evaluate differences in
comorbidity prevalence for FM, SLE and NIRD compared with RA. As the large
sample sizes result in most differences being statistically significant, we
concentrated on significant differences with an odds ratio ≥1.5 and ≤0.66 compared
with RA. No differences between RA and NIRD reach an odds ratio ≥1.5 or ≤0.66.
However, major prevalence differences are noted between RA patients and those
with SLE and fibromyalgia, as shown in table 1.
Two patterns of increased comorbidity emerge. There is an increase in MI, stroke,
all-cardiovascular diseases, hypertension, pulmonary, renal and neurologic disease
in SLE, as well as an increase in diabetes, fracture, cataract and GI disease. In
fibromyalgia two group patterns emerge, the first being depression, mental illness
and drug/alcohol problems (psychological issues). The second pattern includes
symptom and symptom interpretation-related illnesses, such as asthma, allergies, GI
ulcer, GI symptoms, neurologic and GU symptoms. Of the 27 health symptom
categories in table 1, fibromyalgia patients reported more conditions than those with
RA in 25 instances in table 1, after adjusting for age and sex.
We investigated the increases in comorbidity in SLE and fibromyalgia further using
the summary comorbidity index. Age and sex adjusted comorbidity index scores
were 1.7 (95% CI 1.7 to 1.7) and 1.8 (95% CI 1.7 to 1.8) for RA and NIRD, and
were 2.4 (95% CI 2.4 to 2.5) and 2.7 (95% CI 2.7 to 2.8) for fibromyalgia and SLE.
In addition, figure 1 shows that there is a smooth increase in the index with age in
RA and NIRD participants. However, the level of the comorbidity index remains
about the same in ages 35-84 in those with fibromyalgia and SLE.
Figure 2. The relation of age to four different types of
comorbid conditions. Cancer (a condition that increases
with age but has little relationship with the underlying
rheumatic disease), upper left; Myocardial infarction (MI) (a
condition that increases with age and is related to the
underlying rheumatic disease), upper right; Severe allergies
(a condition which is part of the symptoms or
manifestations of the underlying disease), lower left; and
Depression (a condition that represent lifetime traits or
manifestation of underlying disease), lower right.
As the comorbidity index is a summary measure, we studied individual age–
comorbidity relationships, and identified four patterns. Figure 2, upper left,
demonstrates a type of comorbidity that increases with age, has little relationship
with the underlying rheumatic disease, and is not part of the symptom or disease
manifestation of the underlying disease. Figure 2, upper right is similar to upper
left. However, the increase in MI prevalence in SLE indicates the strong early-inlife relation between SLE and MI. The pattern, lower left, of figure 2 indicates a
condition in which the “comorbidity” is part of the symptoms or manifestations of
the underlying disease. Finally, figure 2, lower right, describes symptoms or
comorbid conditions that represent lifetime traits or manifestation of the underlying
illness. The fall-off in this figure with increasing age is an artifact of left censoring
(patients enrolled later in life). These data suggest that comorbidity indices that
combine comorbidities should not ordinarily be used across diseases.
Summary. Separate patterns of comorbidity are identified in patients with fibromyalgia, SLE, and RA/NIRD. The patterns include the type of comorbid variables
reported and their associations with age and disease duration. Comorbid conditions are most common in fibromyalgia, followed by SLE. Hypertension and GI disorders are
the most common current somatic illnesses, and depression the most common mental illness, with a current depression prevalence of about 15% in RA/NIRD and 34 to
39% in SLE and fibromyalgia. Depression is the most strongly associated correlate of EQ-5D quality of life.