An unusual headache: CSF negative APML relapse in the brain.

Acute Promyelocytic Leukaemia (APML) is a subtype of Acute Myeloid Leukaemia (AML), responsible for around 10% of cases of the disease in adults. Extra medullary disease (EMD) occurs infrequently in APML, but where EMD does occur, the central nervous system is one of the most commonly infiltrated sites. Our case describes a man in his 40s undergoing post-therapy surveillance for APML who presented to follow-up clinic with a headache, which was ultimately found to be caused by a tumour comprised of APML cells. His case presented a diagnostic challenge due to the benign appearances of the lesion on initial computed tomography brain imaging and the non-diagnostic cerebrospinal fluid analysis. The diagnostic difficulties described in our case emphasizes that clinicians working with APML patients must approach new neurological symptoms with a high degree of suspicion to prevent diagnostic delay.