Amyotrophic lateral sclerosis (ALS) is a motor neuron disease characterized by serious muscle atrophy and weakness. The purpose of this study was to find prognostic factors in patients with mild ALS using application forms for the Specified Disease Treatment Research Program in Japan. We classified ALS as mild, moderate and severe. The subjects consisted of 363 patients with mild ALS who underwent needle electromyography at registration and were followed for more than one year. Time to progression to severe ALS and time to deterioration of activities of daily living such as speech dysfunction, upper limb dysfunction, and walking disability were used as outcomes. Cox proportional hazards model analysis was performed to identify prognostic factors. Of the patients with initially mild ALS, 38.3% (139/363) had progressed severe ALS at the last follow-up. In multivariate analysis of time to progression to severe ALS, bulbar onset (hazard ratio [95% confidence interval]: 1.68 [1.13-2.49], p
= 0.010), tongue atrophy (1.69 [1.14-2.51], p
= 0.009), dyspnea (1.57 [1.02-2.41], p
= 0.042) and active denervation findings (ADFs) of the cervical-upper limb area (1.81 [1.25-2.63], p
= 0.002) emerged as prognostic factors. Furthermore ADFs in the trunk area were prognostic factors for upper limb dysfunction and walking disability (1.72 [1.05-2.81], p
= 0.031, and 1.97 [1.09-3.59], p
= 0.026). In conclusion ADFs of the cervical-upper limb area and trunk area were prognostic factors in ALS patients.
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