How to tell if bony growth on big toe base is a bunion, osteoarthritis, or rheumatoid arthritis or gout/tophi? only on right foot.

X-ray will help: As will your clinical history and exam. Goit is a diagnosis made largely by a blood test though gouty drpisits that are not invled or tophi do occur they often are very obvious and shoe up with x-ray too. Bone spurs from trauma can be commun in the big toe and many sports related issues can lead to mild DJD in the big toe. Ra is a DX that can be present though less likely to appear in only bone.

See a rheumatologist: A rheumatologist is an expert in musculoskeletal medicine who can distinguish between the diagnoses you mention by asking questions, examining the toe, and doing tests if needed (x-ray, bloodwork, ultrasound etc). Bunions are slow growing and hard. Oa is more common >age50 and chronically stiff. Tophi usually softer, +/- yellow and go with sudden flares (red, swollen, painful), and RA symmetric.

See a podiatrist: Go see a podiatrist. Gout would flare up and you have intense pain. Arthritis is due to joint space narrowing which is very possible. Ra 36 yo male not likely and it is on both side, bunion is a possibility. Usually if the bony growth on the side of the big toe joint its a bunion. Top of the big toe joint is arthritis. Podiatrist can tell you exactly what you got and how to take care of it.