It is known to be associated with other autoimmune diseases, like spondyloarthropathies and psoriasis (thought to often precede psoriatic arthritis).

A common autoimmune enthesitis is at the heel, where the Achilles tendon attaches to the calcaneus.

[3][4] Early clinical manifestations are an aching sensation akin to "working out too much", and it gets better with activity.

The muscle insertion hurts very focally as it joins into the bone, but there is little to no pain at all with passive motion.

Symptoms include multiple points of tenderness at the heel, tibial tuberosity, iliac crest, and other tendon insertion sites.