T2 FLAIR Increased Signal Intensity at the Posterior Limb of the Internal Capsule: Clinical Significance in ALS Patients

Abstract

Amyotrophic lateral sclerosis (ALS) is characterized by progressive upper and lower motor neuron degeneration. A hyperintense signal on T2-weighted images along the corticospinal tract has been reported in patients with confirmed ALS. However, the specificity of this finding is under consideration, since it is also identified in healthy controls. Moreover, the correlation of this finding with disease progression has not yet been established. The purpose of our study is to evaluate the frequency with which this high signal appears in the posterior limb of the internal capsule (PLIC), compare visual with quantitative measurements, and correlate these with the progression of the disease. Our prospective clinical study included 24 patients and 51 healthy volunteers. In the ALS patient group, the diagnosis was established according to the criteria of El Escorial in the revised form of Airlee House. All patients were neurologically examined and underwent diagnostic procedures to exclude other diseases resembling ALS. The initial MRI was performed six months to two years after the onset of symptomatology. All ALS patients were clinically examined regarding their symptoms from the upper and lower motor neurons. Follow-up MRIs were performed in nine out of 24 patients over a period of six months. Signal changes in the PLIC are visually evaluated on FLAIR images, and are classified as distinct, mild or no signal change. Fractional anisotropy (FA) measurements are performed by placing a region of interest (ROI) in the PLIC bilaterally. Both findings are being compared. Mild signal changes were visualized in the PLIC in ten volunteers and seven patients. Distinct T2 FLAIR signal changes were visualized in the PLIC in seven ALS patients. No distinct signal change was visualized in the controls. Moreover this increased T2 FLAIR signal change became more accentuated with disease progress. FA measurements in patients were lower than in age-matched healthy subjects, with a further decrease with disease progression. Our findings indicate that although mild hyperintensity of the PLIC is not pathognomonic for ALS, detection of a distinct PLIC hyperintensity that gradually accentuates might actually be a sign of progressive ALS. This finding is supported by the progressively decreasing FA measurements. Larger numbers of patients need to be included and re-evaluated to obtain statistically significant results.