Background: Involvement of metals or silica in the pathogenesis of sarcoidosis has been suggested by several case reports and specific epidemiological studies. However, the combination of occupational exposure and an immunological reaction has not been studied before in a group of sarcoidosis patients and non-sarcoidosis controls. Methods: In 256 sarcoidosis patients and 73 control patients with obstructive sleep apnea, exposure to metal and silica was assessed using a questionnaire consisting of a complete occupational history subsequently linked to jobexposure matrices. Next, immunoreactivity to aluminium, beryllium, zirconium and silica was determined in 33 sarcoidosis and 19 control patients using a lymphocyte proliferation test. Results: In sarcoidosis, 83 out 256 patients (32.4%) had occupational exposure to metals or silica, compared to 24.7% in the control group (p = 0.21). A significantly higher percentage of the sarcoidosis patients tested showed immunoreactivity to metals or silica compared to the control group (21.2 and 0% respectively, p = 0.039). Conclusions: Immunoreactivity to silica and metals was only found in sarcoidosis patients, supporting the hypothesis that these antigens may be involved in the pathogenesis of a distinct subgroup of sarcoidosis patients. This indicates that when searching for causative agents in sarcoidosis patients, besides beryllium, also zirconium, aluminium and silica deserve clinical investigation.

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A diagnosis of silicosis is made on the basis of exposure and typical radiological findings, according to the ILO's International Classification of Radiographs of Pneumoconiosis. Radiological patterns of silicosis can, however, resemble sarcoidosis. Sarcoidosis is a multi-systemic disorder of unknown etiology, although a role for initiating inorganic triggers such as metals or silica has been suggested. In this case report, we illustrate a patient previously diagnosed with silicosis based on exposure and radiological features, progressive under immunosuppressive treatment. In view of these findings, an open lung biopsy was performed and revealed sarcoidosis. The patient was effectively treated with infliximab. Further analysis showed the presence of silica in the granulomas. Sensitization to silica was also demonstrated, suggesting an association between silica exposure and sarcoidosis in this patient.

BackgroundSeveral studies demonstrated that Propionibacterium acnes (P. acnes) may be involved in sarcoidosis pathogenesis. Presence of P. acnes was found in granulomas of the majority of Japanese sarcoidosis patients. However, presence of P. acnes in tissue has never been related to sarcoidosis phenotypes and clinical outcome. Therefore, the aims of our study were to demonstrate whether P. acnes can be detected in granulomas of Dutch sarcoidosis patients and to investigate whether its presence is related to a clinical phenotype and/or course of disease.MethodsSections of formalin fixed paraffin-embedded tissue blocks of 76 sarcoidosis patients were examined by immunostaining with a P. acnes-specific monoclonal antibody (PAB antibody) using a VENTANA BenchMark ULTRA. Clinical outcome status (COS) was determined and classified into two phenotype groups: A: resolved, minimal or persistent disease without treatment (COS 1–6) and B: persistent disease with need for treatment (COS 7–9).ResultsP. acnes was detected in samples of 31 patients (41%) and located within granulomas in samples of 13 patients (17%). The frequency of P. acnes detected in granulomas at diagnosis was significantly higher in patients with phenotype B compared to patients with phenotype A (29% versus 0%, p=0.021).ConclusionPresence of P. acnes in granulomas can be confirmed in Dutch sarcoidosis patients. It is intriguing that presence of P. acnes in granulomas is more frequently found in patients with chronic disease requiring treatment. This adds to the rationale that a subgroup of sarcoidosis patients might benefit from antibiotic therapy.

Elevated Serum Amyloid A (SAA) levels have been found in several inflammatory diseases, including sarcoidosis. SAA is suggested to be involved in sarcoidosis pathogenesis by involvement in granuloma formation and maintenance. We hypothesized that SAA serum levels would be higher in sarcoidosis compared to other non-infectious granulomatous and non-granulomatous diseases. SAA levels were measured in serum from sarcoidosis, Hypersensitivity pneumonitis (HP), and (eosinophilic) granulomatosis with polyangiitis ((E)GPA) patients. Idiopathic pulmonary fibrosis (IPF) patients were included as non-granulomatous disease group. SAA levels of patients with sarcoidosis (31.0 µg/mL), HP (23.4 µg/mL), (E)GPA (36.9 µg/mL), and IPF (22.1 µg/mL) were all higher than SAA levels of healthy controls (10.1 µg/mL). SAA levels did not differ between the diagnostic groups. When SAA serum levels were analyzed in sarcoidosis subgroups, fibrotic sarcoidosis patients showed higher SAA levels than sarcoidosis patients without fibrosis (47.8 µg/mL vs. 29.4 µg/mL, p = 0.005). To conclude, the observation that fibrotic sarcoidosis patients have higher SAA levels, together with our finding that SAA levels were also increased in IPF patients, suggests that SAA may next to granulomatous processes also reflect the process of fibrogenesis. Further studies should clarify the exact role of SAA in fibrosis and the underlying mechanisms involved.