The significance of prolactin in systemic connective tissue diseases

Does prolactin (PRL) level testing in the diagnosis of systemic connective tissue diseases make sense and should we test it in everyday practice?

Connective tissue diseases (CTDs) are a group of heterogeneous disorders, involving multiple body systems. Rheumatoid arthritis (RA) is one of the most common connective tissue diseases with a global prevalence of 0.3-1% and can be inherited. Less common are systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), systemic sclerosis (SSc), primary Sjögren's syndrome (pSS) and inflammatory myositis. Prolactin is responsible for lactation, breast growth and many other bodily processes, and is elevated in blood of woman who are pregnant or breastfeeding. Hyperprolactinemia is relatively common in women, so some rheumatic diseases may be caused by high prolactin levels, and it should be detected during diagnosis.

Prolactin signals are found in arthritic joint tissues (chondrocytes and synovial fibroblasts) to inhibit cartilage degradation, synovitis and osteoclastogenesis. On the other hand, hyperprolactinemia also promotes the conversion of PRL to vasoinhibin, a fragment of PRL that directly stimulates and indirectly inhibits arthritis in a cell type-dependent manner. The role of the PRL/vasoinhibin axis in inflammatory arthritis should still be monitored and further research is needed to help elucidate the role of PRL in rheumatic diseases in order to ultimately develop new therapeutic interventions that can be tested in patients.

Nowadays, there are no clear indications for prolactin testing in the diagnosis of systemic connective tissue diseases. In the case of suspicion or confirmation of some systemic connective tissue diseases, such as rheumatoid arthritis or systemic lupus erythematosus, testing the prolactin level makes sense when severity of disease symptoms is observed.