Talk to Rheumatologist on Arthritis Or Auto Immune Type Whole Body Joints Affected

My brother is having pain symmetrical in all body joints. It started with wrist and major joints but now in fingers and toes, neck spine. Appears cartilage is wasting away and feel like walking on marbles under feet. Bloods have come back as fine and very minor arthritis showing in wrist Xray. No major inflammation in bloods. Started maybe with change to a healthy diet or working with toxins. It feels like something is eating away and attacking his body and becoming like jelly. What advanced test can be done for diagnosis.? Could it be auto immune type disease/ lipids disease/ lack of something in diet. Is progressing too fast and need someone who can look at alternative solutions also. Thanks Samina