Melissa Wright, MD, PhD, discusses how to evaluate hypotonia and weakness in infants and recognize clinical signs that may raise suspicion for SMA.
What patterns and developmental cues are crucial to a floppy infant diagnosis?
Transcript
The floppy infant is a problem that every pediatrician will face at some point in their career. It can be really challenging because the differential is really, really broad.
It’s even harder because we know that some causes, like SMA, are treatable and it’s important to treat them early, so we really don’t want to miss them.
When I’m evaluating a floppy baby, there are a couple of questions that I like to ask that can help to categorize where the problem is.
These are questions like the timing. “Is the hypotonia getting worse over time? Is it progressive? Or is it staying about the same or even getting a little bit better? Is the baby hypotonic with normal strength, or is the baby hypotonic and weak?”
And then I like to think about cognition. “Is the baby encephalopathic? Are they particularly sleepy, or are they having trouble with cognitive development? Or are they bright and alert and playful and learning well? Are reflexes normal, decreased, or increased?”
A floppy baby who has encephalopathy or is having trouble with cognitive development, who has nonprogressive hypotonia, their strength is normal or mildly decreased and they have normal or increased reflexes, probably has a central nervous system cause for their hypotonia.
But on the other hand, a baby with progressively worsening hypotonia and weakness who’s otherwise bright and alert and playful and interactive but has decreased or absent reflexes should really raise suspicion for SMA.
If you’re able to see tongue fasciculations, then SMA should be far and away the highest thing on your differential. However, tongue fasciculations can be hard to see, so if you don’t see them, I wouldn’t take SMA off of your differential and I would still look for it if you’re suspicious.
It’s really important to note that some kids with SMA will be missed on the newborn screen, so a negative newborn screen doesn’t rule out a diagnosis of SMA, and you should still send testing if you’re suspicious.
