I am sorry to hear about everything that your pet has been going through. This is always so difficult and low platelets can be so scary.
I assume that we have suspended metacam use while on prednisone? Other pain medications like tramadol may be safer with concurrent use of prednisone, if we need pain medications.
Autoimmune disorders can lead to low platelets - ITP Immune Thrombocytopenia is not uncommon. Steroids or other immune suppressives like azothioprine are often used. Other tests like radiographs and ultrasounds are important to rule out other underlying diseases. Also blood tests if indicated may also be helpful to rule out diseases like Ehrlichia which can also lead to ITP. So far I have not heard that helicobacter is a causative agent for thrombocytopenia in dogs.
I would recommend regular platelet checks until we are 1) out of a danger zone and 2) are on an upward trend.
I hope that this helps.
Christopher A. Lee, D.V.M., C.V.L.S.
Promoting surgical options and pet comfort through the use of lasers.