How do you interpret small joint effusions seen on ultrasound without power doppler signal in the setting of compatible inflammatory symptoms (i.e morning stiffness)?

It certainly increases probability of Inflammatory arthritis, if aligns with clinical symptoms.

I would check inflammatory markers, autoimmune serologies, infectious work up and all to determine type of arthritis and consider prednisone trial and likely consider immune suppressive regimen based on r...

Can also keep in mind that medication use, including NSAID use, can affect the Doppler signal as well. See Ahmed et al., PMID 21803749