I had a rash on my arm so I went to the dermatologist, but I was diagnosed with an unknown cause.
「腕に発疹が出たので皮膚科に行ったが原因不明と診断された。」は英語で「I had a rash on my arm so I went to the dermatologist, but I was diagnosed with an unknown cause.」という意味があります。
腕ーArm
発疹ーRash
皮膚科ーDermatologist
原因不明ーUnknown cause
診断するーTo diagnose
I went to a dermatologist because I developed a rash on my arm, but the cause is unknown.
「腕に発疹が出たので皮膚科に行ったが原因不明と診断された」と言いたい場合、「I went to a dermatologist because I developed a rash on my arm, but the cause is unknown.」と表現できます。
「dermatologist」は「皮膚科医」、「rash」は「発疹」、「unknown」は「原因不明」という意味です。