The diagnostic value of midbrain hyperechogenicity in ALS is limited for discriminating key ALS differential diagnoses

BACKGROUND Hyperechogenicity of the substantia nigra was recently reported in patients with sporadic ALS with a frequency similar to PD. Data on the diagnostic utility compared to key differential diagnoses of ALS do not exist yet. METHODS We prospectively enrolled 43 patients with ALS, 29 with myasthenia gravis, 25 patients with inflammatory neuropathy, and 13 with cervical canal stenosis. All patients were examined by a blinded investigator using transcranial B-mode sonography planimetrically measuring hyperechogenic areas of the midbrain representing the substantia nigra. RESULTS Mean midbrain hyperechogenic area was increased in ALS compared to non-ALS differentials. ROC analysis revealed only small area under the curve for detecting ALS (AUC: 0.669 [95%CI: 0.56-0.78]; p = 0.006). Highest Youden index was observed for area size of <0.14 cm(2) (Youden index: 0.28). Using this cut-off score and that generated from normative data of healthy controls, area size measurements provided a sensitivity of only 46-58% and specificity of 69-83% for detecting ALS. No correlations of hyperechogenic area sizes in ALS patients were found to age, gender, ALS subtype (bulbar versus spinal form), disease duration or ALS-FRS-R score. CONCLUSIONS Midbrain hyperechogenicity is reproducibly found in ALS patients, but its diagnostic value for discriminating ALS from its key differentials is limited.