Recently, controversy regarding the classification of BD under SpA has arisen for two main reasons: firstly, there may be a common immunopathological pathway involved in BD, ankylosing spondylitis (AS) and psoriatic arthritis (PsA), such as IL-10, IL-17 and IL-23; secondly, the acne–arthritis–enthesopathy cluster of BD is associated with SpA-related symptoms [14]. Here, IL17A is linked to Behcet disease.