Recent studies that have used beta-CIT-single-photon emission computed tomographic (SPECT) or 18F-Dopa positron emission tomographic (PET) imaging to assess the progression of dopamine neuron loss in PD have found that approximately 10% to 15% of subjects thought to have early PD diagnosed by clinical criteria have normal scans. These individuals have been termed "subjects with scans without evidence of dopaminergic deficit" (SWEDDs). It is not clear whether these patients have very early PD, some previously unrecognized form of PD, or do not have PD. Understanding this situation has implications regarding the sensitivity of such imaging studies to diagnose early PD and our ability to accurately diagnose early PD with clinical criteria.
Marek and coworkers reported the 4-year follow-up study of a cohort from the Earlier vs Later L-Dopa (ELLDOPA)-CIT study. Patients whose initial scans demonstrated a dopaminergic deficit (non-SWEDDs) showed a progressive decline in beta-CIT uptake, as expected. At baseline as well as 9, 18, 36, and 48 months, putamenal beta-CIT uptake was 40%, 39%, 37%, 35%, and 31% of that seen in normal, age-matched controls. By contrast, SWEDD subjects demonstrated normal beta-CIT uptake at baseline and throughout the study. At baseline as well as 9, 18, 36, and 48 months, SWEDD subjects had putamenal beta-CIT uptake of 111%, 105%, 105%, 110%, and 112% of values found in normal, age-matched controls. This suggests that patients with a baseline SWEDD comprise a distinct population, and probably do not have PD. These investigators suggested that dopaminergic imaging should be considered an inclusion criterion for future studies to assess the progression of disease in early PD. An analysis of the videotapes of SWEDD subjects is under way to determine whether SWEDD subjects can be distinguished from non-SWEDD subjects at baseline on the basis of clinical features.