People fear that eye twitching is the first sign of ALS, but oddly, the eye muscles never become paralyzed by ALS.
Right to the very end, the paralyzed ALS patient who can’t even breathe on their own can still blink their eyes: muscle control.
Researchers at Umeå University in Sweden have investigated this perplexing fact.
One might think that the very tiny size of eye muscles might be the reason they don’t become paralyzed as ALS worsens, but if this were the reason, lip and tongue movement would also be preserved. But this is not the explanation.
The muscles of the eye are not the same as those in your limbs or fingers. For instance, one difference is in their neuromuscular junctions that are formed between the muscle fibers and nerve cells.
It is not clear if ALS begins in the cell body or the nerve connection, says Anton Tjust, author of the dissertation that attempts to explain why eye muscles don’t lose their function from ALS.
Tjust is a doctoral student at the Department of Integrative Medical Biology and the Department of Clinical Sciences at Umeå University.
In the early stages of ALS, the loss of connection between muscles and nerves is seen. However, there is some kind of protection mechanism for the eye muscles.
Tjust was part of a previous study that, along with his latest one, attempted to explain why ALS does not paralyze eye muscles.
The prior study revealed that there are certain muscle fiber types in the eye that apparently decrease in quantity as ALS progresses.
One of the fiber types is called “multiply-innervated.” In up to 30 percent of patients it was decreased in number.
“It seems like certain muscle fibre types in the eye muscles are not at all resilient to ALS,” says Tjust’s dissertation. “It is rather other fibre types in the eye muscles that preserve their functions so well.”
These “other” fiber types have not been identified.
Voluntary muscles (those you can move upon will) contain stem cells. It’s believed that the stem cells in eye muscles are more efficient than those in the limbs. The mechanism, if this is true, of course is not known.
But the researchers speculate that the eye muscle stem cells are somehow involved in the retention of movement while ALS destroys movement elsewhere. Another speculation is that stem cells in the limbs wither away in numbers.
Eye Muscle Stem Cells in Healthy and ALS Subjects
Tjust’s research showed that the overall number of eye stem cells wasn’t much different between ALS patients and healthy controls.
But the study also found that the front part of the eye had an “accumulation of muscle stem cells.”
Limb Stem Cell Comparison
The number of limb stem cells in deceased ALS patients was compared to that in age-matched controls.
Advanced-ALS patients had a normal or increased number of limb stem cells.
But only moderate levels of eye stem cells were round—in both the deceased patients and healthy controls.
The conclusion is that the limb stem cells don’t deteriorate with ALS, and that eye muscle stem cells don’t have much of a role in preventing paralysis in that area.
However, there’s no denying that some sort of protective mechanism is in place, says the dissertation. Why is this? How does it happen?
Tjust and his team plan on continuing their mission to unearth why the eyes do not become paralyzed by ALS. Perhaps the answer to this question will lead to an effective treatment.