Early subjective symptoms include difficulty urinating, but in many cases there are no clear symptoms.
Literal
Early [genitive-の] subjective-symptoms [as-としては], urination-difficulty [subject-が] exists [but-が], many [genitive-の] cases, clearly stated symptoms [subject-が] exist-not.
Medical writing. 自覚症状 ('subjective symptoms,' literally 'self-awareness symptoms') is the technical medical term for symptoms the patient experiences themselves — contrasting with 他覚症状 (symptoms observable by others). 排尿 ('urination,' literally 'discharge-urine') and 障害 ('disorder, impairment') are medical compounds. ~としては ('as for the role of, as') + 多くの場合 ('in many cases') structure the medical generalization.