cryptogenic
/krɪpˈtɒdʒɛnɪk/Definitions
1. adjective
Originating or caused by an unknown or obscure source; mysterious or inexplicable.
“The cryptogenic nature of the illness made it difficult for doctors to diagnose the patient.”
2. noun
A cryptogenic disease or condition, especially one whose origin or cause is unknown or unexplained.
“The patient was diagnosed with a cryptogenic illness that required ongoing treatment.”