Coexistence of sarcoidosis and spondyloarthritis: a rare but intriguing association

To characterise the key epidemiological, clinical, immunological, imaging, and pathological features of the coexistence between sarcoidosis and spondyloarthritis (SpA).

All centres included in two large multicentre registries (the Sjögren Syndrome Big Data Consortium and the Sarco-GEAS-SEMI Registry) identified potential cases of coexisting SpA and sarcoidosis. Inclusion criteria were the fulfilment of the current classification criteria both for SpA (ASAS) and sarcoidosis (WASOG).

We identified twenty-three patients (14 females and 9 males) with a mean age of 44 years at diagnosis of SpA and of 45 years at diagnosis of sarcoidosis. Most of the patients fulfilled the ASAS criteria for axial SpA. In 8 patients, sarcoidosis was diagnosed after SpA, in 9 patients sarcoidosis preceded SpA and in 6 patients the diagnoses were concurrent. Within these groups, the HLA*B-27 haplotype was detected in 5 (62%), 2/8 (25%) and 3 (50%) of patients respectively. A median of 2 years (range 1-19) occurred between the diagnosis of the two diseases in the first 2 groups. Lung, skin, and extra-thoracic lymph nodes were the most frequent sarcoidosis manifestations in all 3 groups.

We have characterised 23 patients who fulfilled the current classification criteria for both SpA and sarcoidosis. Therefore, sarcoidosis may coexist with SpA like other systemic autoimmune diseases, and this may be explained by shared pathogenic mechanisms. Since Th17 cells are leading actors in the pathogenesis of both SpA and sarcoidosis, these cells may be the missing link connecting the two diseases.