The inflammatory markers many times are not raised initially and thus need to be repeated. You would need the following;
1) HLA B 27.
2) X-rays and MRI of the sacroiliac joint and lumbar spine.
These two are cardinal to diagnose spondyloarthropathy/psoriatic arthritis.
You would also need the following;
a) Sedimentation rate.
b) Serum uric acid
c) RA factor
d) Antinuclear antibodies.
MRI of the foot also is advised.
The steroid shot in the toe is likely to help. Plantar fasciitis can be managed by;
1) Moist heat or ice compresses; whatever suits you
2) Anti-inflammatory analgesics like Ibuprofen
3) Local analgesic ointment /spray
4) Physical therapy
5) Deep electrotherapy like iontophoresis, phonophoresis, short wave diathermy, electrical stimulation, etc.
6) Consideration of steroid shot
7) Shock wave therapy
8) Custom-fabricated inserts
There is a new therapy called autologous blood injection in which your own blood is injected at the pain site, which is said to be quite effective. Shock wave therapy is available in sport medicine clinics or physical therapy clinics. This too is supposed to help in the resistant cases.
I wish your symptoms resolve soon.
I would be happy to assist you further if you need any more information.
Thanks for using Just Answer.