Amyotrophic lateral sclerosis (ALS) is most often a sporadic disorder that affects both upper and lower motor neurons. Because the prognosis of ALS is uniformly poor compared to other motor neuron disorders, defining the diagnosis can help guide appropriate clinical management and improve quality of life for patients. However, the diagnosis of ALS is often challenging and there may be overlapping clinical features with other rare diseases. We present four patients who were referred to our center because of the clinical suspicion of ALS, in whom more detailed assessments revealed an alternative diagnosis, and we discuss the limitations of the modified-El Escorial criteria.