Concomitant rheumatoid arthritis and amyotrophic lateral sclerosis: report of two new cases and review of literature.

To describe a rare association between rheumatoid arthritis (RA) and amyotrophic lateral sclerosis (ALS). Two new cases of patients with RA who developed amyotrophic lateral sclerosis (ALS), one receiving anti-TNFα agents, were reported. Only other five cases of this rare association have been previously described in literature. The simultaneous presence of the two diseases represents a difficult diagnostic challenge because RA may mimic some musculoskeletal symptoms of ALS. There is no evidence in favor of a common pathophysiologic mechanism, and thus the possibility of a fortuitous association must be raised. A neurotoxic side effect of various drugs for RA treatment could be considered. Casual or causal association remains a difficult choice. The possibility of a coincidental association must be raised but neurologic side effects of TNFα blockers lead to discussion.