Comparative analysis of DaT scan imaging and cutaneous phosphorylated alpha-synuclein (PSYN) deposition in patients with suspected Parkinson Disease (PD).

There is no gold standard for the diagnosis of PD. The DaT scan complements the clinical diagnosis in some patients with PD. Recent reports suggest that detection of cutaneous PSYN is a specific and sensitive test in patients with PD and other alpha-synucleinopathies.  The relative contribution of these tests to the diagnosis of PD is not known.

Seventeen patients from a private practice movement disorder practice were recruited. All participants had a clinical question of a parkinsonian syndrome, a prior DaT scan, and had been treated with carbidopa/levodopa.  Responses to therapy were document by the treating physician for all patients. Biopsies were taken from the posterior cervical region, distal thigh and distal calf and were were stained with antibodies against PGP9.5 and PSYN. The investigators reading the biopsies were blinded to the DaT scan results and the response to treatment.  Results of DaT scans, phosphorylated alpha-synuclein staining and clinical diagnoses were compared.

The DAT scan and PSYN staining revealed concordant results in 9 patients.  Six patients had concordant ‘negative’ results with normal DaT scan, no response to carbidopa/levodopa, and negative PSYN on biopsy staining.  Three subjects had concordant ‘positive’ results with an abnormal DaT scan, good response to treatment, and deposition of cutaneous PSYN supporting a clinical diagnosis of PD.  Eight patients had an abnormal DaT scan with no evidence of cutaneous PSYN deposition and no response to carbidopa-levodopa, suggesting a clinical diagnosis other than PD. 

These data support the sensitivity and specificity of the measurement of cutaneous alpha-synuclein in patients with a parkinsonian syndrome and suggest that this assessment can contribute to the diagnosis of PD.  Larger prospective, longitudinal studies are indicated to compare these diagnostic tests in parkinsonian patients.