Clinical characteristics and organ system involvement in sarcoidosis: comparison of the University of Minnesota Cohort with other cohorts

Sarcoidosis is a multi-system disease of unknown etiology characterized by the presence of non-caseating granulomas in involved organs [1]. Although lungs, mediastinal and hilar lymph nodes are most commonly involved, sarcoidosis is associated with heterogeneous manifestations, disease severity, and outcomes [1‐4]. The incidence of sarcoidosis is at least 45–300/100,000 individuals in the US [5], of both sexes, and all ages and races [1, 6‐8]. The annual mortality is 2.8/million people [3, 9] and is rising [10] with a more aggressive course and more extrapulmonary involvement reported in black patients [11].

Recently, four high-risk sarcoidosis manifestations were recognized as highly associated with greater morbidity and mortality [12]. These include treatment-resistant pulmonary disease, neuro-sarcoidosis, cardiac sarcoidosis, and multisystem organ involvement. In the US and Europe, respiratory failure is the most common cause of sarcoidosis-related mortality [9, 10]. In contrast, Japanese cohorts have a higher incidence of cardiac disease, and cardiac involvement is the most frequent case of death due to sarcoidosis in Japan [13]. Lofgren’s syndrome, an acute presentation of sarcoidosis associated with fever, erythema nodosum, arthralgias and mediastinal or hilar adenopathy, is more frequent in Scandinavian countries and is associated with a good prognosis [14]. The heterogeneity in sarcoidosis presents challenges in predicting disease course, optimizing treatments, and establishing a uniform standard for organ involvement assessment.

There is significant geographic variability in sarcoidosis manifestations. The variability in sarcoidosis manifestations could be explained by regional variability in sarcoidosis but also could be due to the tools employed for assessment of organ involvement. A number of reports have used the tool developed by the A Case Control Etiologic Study of Sarcoidosis (ACCESS) investigators [15] to assess disease manifestation [11, 16, 17]. This tool was further modified by the World Association of Sarcoidosis and Other Granulomatous Disorders (WASOG) task force to address additional manifestations and possible organs involved with sarcoidosis. The WASOG sarcoidosis organ assessment instrument classifies organ involvement as “highly probable”, “probable”, “possible”, or “no consensus” [18]. Various other assessment tools for sarcoidosis have been proposed. More recently, the Genomic Research in Alpha-1 Antitrypsin Deficiency and Sarcoidosis (GRADS) study classified clinical phenotypes into nine clinical phenotype groups [19], including efforts to define multiorgan, cardiac defining therapy, and other phenotypes.

Our objective is to describe the clinical characteristics of the sarcoidosis cases seen at the University of Minnesota, and to compare the characteristics of our cohort to the ACCESS and other cohorts. The racial distribution of Minnesota residents includes White (83.75%), Black or African American (5.95%), Asian (4.66%), two or more races (2.81%), other race (1.74%), Native American (1.05%), and Native Hawaiian or Pacific Islander (0.04%) [20]. A unique feature of the Minnesota population is the substantially higher percentage of residents of Scandinavian origin which may influence the disease manifestations. While only 0.2% of US population is of Scandinavian origin, up to 1.5% of Minnesota residents self-report a Scandinavian origin, and we presume that our cohort may have this representation [21].

This cohort includes 187 sarcoidosis subjects consented between March 2015 and May 2019 at a tertiary sarcoidosis referral center in Minnesota. The diagnosis of sarcoidosis was made per American Thoracic Society (ATS) statement [1], meeting the following criteria: 1) a compatible clinical and radiologic finding; 2) histological evidence of non-caseating granulomas; and 3) exclusion of other diseases such as infections, common variable immunoglobulin deficiency (CVID), chronic beryllium disease (CBD), and malignancy. Diagnosis dates were determined per biopsy dates and estimated to be June 15th when days and/or months were not available. Subjects without histological evidence were excluded from this cohort. Subjects with a history of malignancy diagnosed within two years prior to or after sarcoidosis were excluded to exclude the possibility of sarcoid-like reactions to malignancies.

We conducted a chart review to collect data on demographics, diagnostics, imaging, past medical history, treatment program, and pulmonary function tests. Racial demographics were collected per patient self-report through the electronic medical record. With limited data, Hispanic whites and non-Hispanic whites were both categorized as “White” in this study. Results from laboratory within one year prior to the initial visit were also collected, including angiotensin converting enzyme (ACE), white blood count (WBC) with differential, soluble interleukin-2 receptor (sIL-2R), C-reactive protein (CRP), immunoglobulin G (IgG), albumin, total protein, liver function tests, calcium, parathyroid hormone (PTH), 25-OH vitamin D, and 1,25-DiOH vitamin D. Scadding stage was established using the closest available imaging study - chest x-ray (CXR) and chest CT topogram if CXR was not available - by an expert independent chest radiologist. The treatment groups, organ involvement, and clinical phenotype were assessed based on the characteristics at enrollment and prior history.

In the absence of histological evidence, the organ system involvement was determined using the ‘highly probable“ and “probable” criteria per the WASOG sarcoidosis organ assessment instrument [18]. Per the WASOG instrument, thoracic involvement includes both pulmonary involvement and thoracic lymph node involvement. One modification we made from the instrument was that although arthralgia was listed under “possible” criteria, we included it for bone-joint involvement when it was associated with Lofgren’s syndrome. Additionally, small fiber neuropathy with positive skin biopsy findings was included for nervous system involvement. In addition to PET, subjects with abnormal signal intensity on magnetic resonance imaging (MRI) of bone marrow were also included for bone marrow involvement.

We established the clinical phenotype groups using the GRADS criteria [19] with minor modifications. Subjects with Lofgren’s syndrome but treated for > 3 months were nonetheless assigned to Acute Sarcoidosis (Group 7). Untreated or treated subjects who were off treatment for at least one year from the visit date were assigned to the Remitting Disease group (Group 8). Subjects with five or more involved organs including cardiac involvement and on systemic anti-inflammatory therapy without remission (not assigned to Group 8) were assigned to Cardiac Defining Therapy (Group 9) as opposed to Multiorgan Disease (Group 1). We identified unclassifiable cases that did not fit any of the GRADS phenotypes, including Stage 0 treated or untreated and Stage I treated.

We grouped the PFT abnormalities into obstructive, restrictive, or mixed obstructive and restrictive ventilatory defects. Obstructive ventilatory defect was defined using Global Initiative for Chronic Obstructive Lung Disease criteria as forced expiratory volume in 1 s (FEV1) / forced vital capacity (FVC) ratio (FEV1/FVC) < 70% and a reduction of FEV1 [22]. Restriction ventilatory defect was defined as FEV1/FVC ratio ≥ 70% and a reduction in FVC. A mixed obstructive and restrictive pattern was defined as FEV1/FVC ratio < 70%, a decrease in FEV1 and total lung capacity (TLC). To simplify the interpretation, the FEV1, FVC, TLC and diffusing capacity of the lungs for carbon monoxide (DLCO) were considered reduced if they were below 80% of predicted values.

Our cohort has similarities and crucial differences compared to previously described cohorts (Table 9). This cohort is primarily composed of cases from upper Midwest and has a higher proportion of blacks and lower proportion of whites compared to the racial distribution of Minnesota residents. With respect to the ACCESS cohort, the age at diagnosis in our cohort was similar, but we observed a higher proportion of males and a lower proportion of black subjects in our cohort. We also observed a higher proportion of extra-thoracic lymph node, eye, liver, spleen, and bone-joint involvement. Other cohorts also reported similarities and differences compared to the ACCESS cohort. A cohort of 166 sarcoidosis cases in Israel was older [17]. Similar to ACCESS cases, more patients in the Israeli cohort were females, and the majority of patients had lung involvement. However, fewer sarcoidosis cases in this cohort had extra thoracic lymph node, liver, CNS, and joints involvement. A small cohort of 21 cases form Mexico was different than the ACCESS cohort with a lower proportion of women and lower median age [16]. This group had more frequent skin and bone marrow involvement and less frequent pulmonary involvement. In contrast, a cohort from the University of California [24] found a higher proportion of cases with neurologic involvement, and another cohort in Olmsted County in Minnesota [25] had fewer cases with eye involvement, but more bone and joint disease. In our cohort, in addition to higher proportion of extra-thoracic lymph node, eye, liver, spleen, and bone-joint involvement, cardiac sarcoidosis, a high-risk manifestation of sarcoidosis, was also more frequent. Given the interaction between the environmental factors and genetics in the pathogenesis of sarcoidosis, regional variations in disease phenotypes may be due to differences in the genetics of the population and/or the nature of the exposure(s) triggering the disease. Because our cohort is drawn from a referral center for sarcoidosis, there may be enrichment for more complicated and advanced cases.

Pulmonary sarcoidosis continues to result in significant morbidity and mortality with rising death rates [10], hospital admissions, and health care costs [2]. It is associated with significantly reduced health related quality of life and symptoms portending the need for treatment and for disease progression [26]. A large proportion of our cases were either stage II/III disease or stage 0 disease, and stage IV primarily fibrotic disease is less common. A substantial proportion of our cases had near normal spirometry and DLCO, and restrictive ventilatory defect was the most frequent finding on pulmonary function testing compared to obstructive and mixed patterns. A large proportion of subjects in our cohort required treatment with anti-inflammatory agents. In the ACCESS incident cohort, lung function was normal in many with FVC > 80% in 69%, yet ~ 47% cases had Scadding stage II/III disease while stage IV disease was present in only ~ 5%. In our cohort, the median and 25th percentile of FVC is 88% predicted and 72% predicted, findings similar to ACCESS. Similar results were also seen for FEV1, and obstructive changes were common with an FEV1/FVC ratio of < 70% in more than 20% of patients. An isolated gas exchange abnormality is not uncommon in sarcoidosis and thus an important clinical outcome. In our cohort, 14.0% had an abnormal DLCO and normal TLC, while 6.6% had abnormal DLCO and normal spirometry, and 17% demonstrated normal DLCO and abnormal spirometry. Thus, patients may demonstrate obstructive, restrictive, mixed patterns or an isolated DLCO. Researchers have commonly used spirometry, DLCO, and chest radiography, to track disease progression in studies [27, 28]. Lung volumes or formal cardiopulmonary exercise testing (CPET) is not routinely used nor is a standard of care in sarcoidosis clinical practice or research as it is more invasive, expensive and normal in many [29]. Patient-reported outcome measures and the six-minute walk test have been recommended in disease assessment [30]. A recent international Delphi study supported multi-faceted outcomes to assess disease severity for clinical and research purposes, including spirometry/DLCO, quality of life, assessment of progression as well as a biomarker [31]. These data support the importance of defining a comprehensive biomarker of disease progression.

A recent NHLBI workshop recognized cardiac involvement as a high-risk phenotype [12, 32]. The proportion of sarcoidosis cases with abnormal advanced cardiac imaging was substantially higher in our cohort than the ACCESS and other cohorts (Table 9), but less than the reported incidence in post mortem studies [33‐35]. Similar rates of increased detection of cardiac sarcoidosis has also been reported by other investigators employing contemporary imaging studies [36‐38]. The utility of these imaging modalities is now widely recognized and incorporated in the diagnostic criteria for cardiac sarcoidosis. The ACCESS criteria did not have advanced imaging criteria, and for the 2006 Japanese Ministry of Health and Welfare (JMHW) criteria, late gadolinium enhancement (LGE) on cardiac MRI was a minor criterion [39] and needed additional criteria to be fulfilled for a diagnosis of cardiac sarcoidosis. In contrast, in the current recommendations by Heart Rhythm Society (HRS), LGE on CMR is sufficient for an adequate clinical diagnosis of cardiac disease in the presence of histologic extracardiac evidence of sarcoidosis [40]. Similarly, for the WASOG organ assessment tool that we used for this cohort [18] and the Japanese Circulation Society Guidelines [41], LGE on cardiac MRI makes the likelihood of cardiac involvement at least probable. Similarly, patchy uptake on a dedicated cardiac PET scan has also been incorporated into the HRS and the WASOG criteria. A crucial element in establishing a diagnosis of cardiac sarcoidosis, even with histology proven extra-cardiac disease, is excluding other causes of LGE, such as coronary artery disease or other non-ischemic cardiomyopathies such as genetic arrhythmogenic cardiomyopathies which could also demonstrate increased myocardial uptake on FDG-PET imaging [42]. Challenges also remain regarding the ideal dietary preparation to suppress normal glucose uptake by the myocardium and avoid false positive FDG-PET. A diffuse uptake of FDG is suggestive of incomplete suppression of physiological glucose uptake in contrast to a patchy or patchy on diffuse uptake that may suggest myocardial inflammatory process [43, 44]. In the absence of a gold standard, as suggested by other groups [45], a multidisciplinary approach is likely to improve the accuracy of diagnosis. The long-term outcomes of cases with abnormal cardiac imaging, especially in cases with no or minimal symptoms and normal heart function, remains unknown.

Extra-pulmonary involvement is presumed to be more common in blacks with sarcoidosis. However despite being a cohort composing of predominantly white cases, our cohort had frequent multisystem disease (using the GRADS criteria and also the WASOG organ assessment tool). We observed more frequent involvement of the skin, extra thoracic lymph nodes, liver, spleen, neurologic, cardiac and bone and joint disease. Of these, neurologic, cardiac, and multisystem disease were considered high-risk manifestations of sarcoidosis due to higher morbidity and mortality. Bone and joint involvement is also a frequent cause of impaired quality of life and often requires systemic anti-inflammatory therapy. We included cases with Lofgren’s syndrome in this category due to our observation of significant morbidity during the acute presentation related to arthralgias, although most of these cases had improvement in symptoms and did not need chronic therapy. As the size of our cohort grows, it will be ideally suited for future studies of high-risk sarcoidosis phenotypes.

We also examined laboratory studies obtained at the clinic visits. Routine laboratory tests were performed for surveillance of drug-related side effects to assess the disease activity with biomarkers and for asymptomatic organ involvement [46]. We identified differences in several analytes in the treated vs. untreated groups and in blacks compared to whites. A higher leukocyte count in treated sarcoidosis cases could reflect an appropriate response to therapy including improved hematopoiesis [47]. Leukopenia as a manifestation of sarcoidosis could be due to bone marrow involvement [48, 49], hypersplenism [50], or lymphocyte redistribution. The T cell redistribution is reported to cause peripheral lymphopenia and is linked to worse severity of the sarcoidosis [51, 52]. We did not observe any difference in the lymphocyte count in the treated vs. untreated and blacks vs. whites. Our cohort is larger in size than the cohort where peripheral lymphopenia was observed and has a larger proportion of cases with lung involvement [52]. Other potential biomarkers of disease activity such as angiotensin converting enzyme [53, 54] and soluble IL-2R levels [55, 56] were also not different in treated vs untreated groups or in whites vs. blacks. The higher level of albumin observed in whites and a higher level of total protein in blacks has been reported previously [57] in these racial groups. Difference in protein fractional patterns could explain a higher IgG level. Various reasons including frequent infections or persistent chronic inflammation could account for the differences in albumin and immunoglobulin levels [58, 59]. Overall, these findings are in line with the findings of other reports that current biomarkers have limited utility for assessing disease activity in sarcoidosis, and highlight the urgent need to develop biomarkers for prognostication and measuring response to therapy [32]. Concurrent to the search for useful serum biomarkers for disease activity, methods for incorporating comprehensive data including other assessments of disease activity, extent of organ dysfunction, and patient reported outcomes, are needed to improve disease severity assessment, prognosis assessment, and guidelines for treatment.

We observed a high proportion of cases that needed systemic anti-inflammatory therapy. Oral corticosteroids are the first-line agents with methotrexate and Imuran as the preferred steroid sparing agent. The dosing of TNF blockers used in sarcoidosis at our center is different than the typical dose for rheumatologic conditions with a maintenance dose of every four weeks (5 mg/kg) for infliximab, in line with the current experience-based recommendations [60].

Despite the retrospective nature of our study, this cohort description provides new insights into regional variability of sarcoidosis as it represents the clinical manifestation in residents of the upper Midwest. Our cohort is a mixed population of incident and prevalent cases and might be a more appropriate representation of sarcoid-related morbidity as opposed to a cohort of newly diagnosed cases. For assessment of pulmonary function testing, we used percent predicted values to assess lung function abnormalities. The other option of using percentile cutoff might be more appropriate, but we do not have this information on all the participants in our study. We also acknowledge that not all the cases in our cohort had all the data points that we presented. As our cohort size grows, we expect the missing values to have a lesser impact on the study findings.

Among sarcoidosis cases in our predominantly white Minnesota population, we found a relatively high proportion of advanced and multisystem disease. Lofgren’s syndrome was not common in our cohort despite high percentage of presumed north-European ancestry in our population. Stage II/III pulmonary disease, cardiac disease, multisystem diseases and joint and bone diseases are more frequently detected in this cohort. The analysis of our cohort highlights the lack of utility of serum biomarkers and limitations of pulmonary function tests in assessing prognosis, need for treatment, and disease severity. The higher incidence of cardiac disease, compared to previous cohorts, suggests that cardiac involvement may be under-recognized and highlights the importance of incorporating advanced imaging and a multidisciplinary approach into the evaluation of patients suspected of cardiac involvement. Our cohort is well suited to investigate high-risk sarcoidosis phenotypes, and studying regional variations in disease phenotypes may shed light on disease mechanisms. Incorporating patient reported outcomes in routine care could provide additional insights into indications and outcomes of treatment.