among the patients of the 50s , what was the top four most frequent diagnoses?
select d_icd_diagnoses.short_title from d_icd_diagnoses where d_icd_diagnoses.icd9_code in ( select t1.icd9_code from ( select diagnoses_icd.icd9_code, dense_rank() over ( order by count(*) desc ) as c1 from diagnoses_icd where diagnoses_icd.hadm_id in ( select admissions.hadm_id from admissions where admissions.age between 50 and 59 ) group by diagnoses_icd.icd9_code ) as t1 where t1.c1 <= 4 )