The diagnosis of PON is challenging, and the most appropriate workup remains unknown. A blood sample was sent to the laboratory of Charles Thirkill, PhD, at the University of California, Davis, with initial positive results on the vasculitis assay, but confirmatory testing for autoantibodies could not be completed due to insufficient sample. However, it is clear that the absence of autoantibodies such as collapsin response mediator protein 5 IgG or the absence of neurological deficits (as in this case) does not rule out its diagnosis, and whole-body imaging should be performed in suspected cases. In this latter regard, several studies have reported that PET and CT scanning is superior to conventional imaging for detection of primary and metastatic lesions. Scanning with PET and CT uses fluorodeoxyglucose, a radioactive isotope that is taken up by actively growing and metabolically demanding cells. In disseminated carcinoma of unknown primary, Sève et al5 found that 41% and 37% of patients had a primary or metastatic tumor, respectively, that was detected on PET scanning but was undetected on conventional imaging.