Amyotrophic lateral sclerosis (ALS) is classified as a motor neuron disease (MND) that can present with both upper and lower motor neuron signs. Concurrent ALS and frontotemporal dementia (FTD) is also a well-known phenomenon. Examples of other primary disorders mimicking ALS or ALS-FTD have been reported in the literature and recognition of these entities is important to ensure proper clinical management. We present here an unusual case of an 86-year-old male patient, clinically diagnosed with ALS and severe cognitive impairment thought to be due to FTD. Postmortem neuropathological examination of his brain and spinal cord did not reveal the typical findings of ALS or FTD. Rather, it revealed multiple non-ALS pathologies including argyrophilic grain disease (AGD), cerebrovascular disease, and Alzheimer’s type pathology. This case raises the possibility that mixed pathologies could mimic motor neuron disease.