What is the sensitivity of Dopamine Transporter (DAT) scan for Multisystem Atrophy?

Sensitivity of DAT Scan for Multiple System Atrophy

DAT scan has limited sensitivity for diagnosing Multiple System Atrophy (MSA), with reported sensitivity ranging from 64-83% depending on MSA subtype and disease duration. 1, 2

DAT Scan in MSA: Diagnostic Performance

• DAT scan (dopamine transporter imaging) shows abnormal patterns of dopaminergic depletion in MSA, similar to other parkinsonian syndromes 1
• Sensitivity varies by MSA subtype:
  • MSA-C (cerebellar type): 64% sensitivity in patients with "possible" MSA-C 2
  • MSA-P (parkinsonian type): Higher sensitivity (83%) in patients with "probable" MSA 2
• Important limitation: DAT scan cannot reliably distinguish MSA from other parkinsonian syndromes like Parkinson's disease (PD) or Progressive Supranuclear Palsy (PSP) 1, 3

Patterns of Dopaminergic Depletion

• In MSA-P, DAT binding is typically reduced by 40-48%, primarily targeting the putamen contralateral to the clinically predominant side 4
• This pattern is less severe than in advanced PD (which shows 63-70% reduction) 4
• Recent research shows no significant differences in DAT binding patterns between MSA-P and PD, making differentiation challenging 3, 5

MRI vs. DAT Scan for MSA Diagnosis

MRI is superior to DAT scan for diagnosing MSA and differentiating it from PD:

• MRI findings specific to MSA include:

  • Putaminal atrophy with reduced putamen/caudate volume ratio (<1.6) 1
  • Brainstem atrophy, particularly in the pons 1, 6
  • "Hot cross bun" sign in the pons (specific to MSA-C) 1
  • Infratentorial signal changes 6

• MRI diagnostic performance:

  • Sensitivity: 73% on 0.5T MRI and 88% on 1.5T MRI 6
  • Specificity: 93-100% compared to PD and controls 6
  • Positive predictive value: 85-93% 6

Clinical Implications

• DAT scan should not be used in isolation for MSA diagnosis due to its limited sensitivity and inability to differentiate between parkinsonian syndromes 1

• DAT scan is most useful for:

  • Confirming the presence of nigrostriatal dopaminergic degeneration 1
  • Early disease detection (particularly in MSA-C patients with shorter disease duration) 2
  • Differentiating parkinsonian syndromes from mimics like essential tremor or drug-induced parkinsonism 1

• A multimodal approach combining MRI and DAT scan provides the most accurate diagnosis 1

• A negative DAT scan does not exclude MSA diagnosis, especially in early disease stages 2

Pitfalls and Caveats

• DAT scan sensitivity increases with disease duration but is less useful in early MSA 2
• False negatives are more common in MSA-C than MSA-P 2
• The American College of Radiology recommends considering clinical features alongside imaging findings for accurate MSA diagnosis 1
• Combining DAT imaging with other modalities (D2 receptor imaging, perfusion studies, MRI) may provide more specific diagnostic information 1