Researchers from Japan led by Takemori Yamawaki, MD, reported the rare case of a 71-year-old man with spinal muscular atrophy (SMA) type 3 who was also diagnosed with myasthenia gravis (MG). 

The man who was diagnosed with SMA type 3 in his 20s presented with dysphagia, which appeared a few months after he started having problems flexing his elbow. When he was referred to the hospital, he was having problems eating.

The doctors investigated conditions that could cause dysphagia. Blood tests revealed he was positive for acetylcholine receptor antibodies and treatment with the reversible acetylcholinesterase inhibitor edrophonium yielded positive results.

He was therefore diagnosed with myasthenia gravis and treated with intravenous methylprednisolone, pyridostigmine, and tacrolimus. This led to the gradual recovery of his dysphagia and he could eat a full meal.

Read more about myasthenia gravis

“When the muscle weakness progresses and dysphagia appears subacutely in SMA type III patients, it is necessary to consider the complications of other diseases such as [myasthenia gravis],” said the authors of the study that was published in Clinical and Experimental Neuroimmunology.

SMA is caused by a mutation in the SMN1 gene which encodes the SMN protein that is essential for the survival of motor neurons. There are different types of SMA, with type 1 being the most severe and type 4 the least severe. It is thought that the copy number of a second homologous gene called SMN2 could play a role in disease severity alongside other genetic factors.

Myasthenia gravis is an acquired, autoimmune disease affecting the neuromuscular junction caused by an immune attack against acetylcholine receptors in the neuromuscular junction.

Edrophonium has served as a diagnostic tool for myasthenia gravis since the early 1930s as it results in a quick and short-lived increase of acetylcholine in the neuromuscular junction.

Reference

Ishikawa R, Sugimoto T, Abe T, et al. Double trouble: a case of spinal muscular atrophy type III found to be complicated by myasthenia gravis due to subacute dysphagia. Clin Exp Neuroimmunol. Published online May 16, 2022. doi:10.1111/cen3.12707