He is a world-renowned osteologist.

He is an expert in osteology.

My grandfather is suffering from arthritis.

My younger brother had an appendectomy yesterday.

My younger sister is missing school because of tonsillitis.

I went to the doctor because of sinusitis.

My father was diagnosed with uveitis.

He was hospitalized due to meningitis.

If you don't have regular dental check-ups, you may develop periodontitis.

He is receiving treatment for folliculitis.