Evaluation of the Hypotonic Infant

00:01 And so, this case in this patient really brings up an important discussion of the differential for evaluation of hypotonia in infancy or evaluation of a floppy baby.

00:13 And we can see conditions throughout the nervous system that can present with hypotonia.

00:18 Central nervous system disorders can cause neonatal hypotonia, chromosomal disorders, metabolic diseases, spinal cord injuries, cerebral dysgenesis, abnormalities in the formation of various cerebral structures and even hypoxic-ischemic injuries in the perinatal and postnatal period.

00:37 Typically, these also present with other prominent findings that would point us in the direction of a central nervous system disorder.

00:44 Importantly, we usually think of hyperreflexia as reflecting central nervous system disorders and that is often not present in the neonate.

00:53 And so central nervous system conditions should be included in the differential diagnosis of hypotonia in infancy or a floppy baby, a weak floppy, reduced tone in a neonate.

01:04 Also, motor neuron disorders and spinal muscle atrophy is an important condition as a motor neuron condition that presents with congenital floppy baby, a hypotonic infant.

01:16 And there are a number of different types of spinal muscle atrophies that we'll be focused on in a subsequent lecture.

01:22 Nerve conditions really rare neuropathies can present with hypotonia congenital hypomyelinating neuropathy, familial dysautonomia, and infantile neuroaxonal degeneration, which are very rare conditions.

01:35 Things you may just need to have heard of but not understand precisely.

01:39 Neuromuscular junction disorders can cause weakness.

01:42 Again, the neuromuscular junction is critical for movement and motor function and abnormalities in the neuromuscular junction in the neonate can present with neonatal hypotonia.

01:51 And that would be congenital myasthenia gravis from a channelopathy or transient neonatal myasthenia.

01:58 From a mother that has myasthenia and those antibodies are able to cross the placenta and remain in the neonate during that initial several days or weeks and then gradually improve.

02:10 And then infant botulism, again, very rare but important to consider.

02:14 And the last group of conditions that should be considered on the differential for a neonate, or an infant with hypotonia are muscle conditions, problems with the muscle.

02:23 And there are two that we're going to focus on in this lecture that are very important.

02:27 And that's congenital muscular dystrophies and congenital myopathies.

02:32 And we're going to walk through the differences between those two.

02:35 In both we have a muscle disorder, so it's a muscular dystrophy, a problem with a muscle or a congenital myopathy, a muscle problem.

02:42 The muscular dystrophies are degenerative, that's what's going on in the muscle.

02:46 And so we see degenerative findings, and those conditions progress over time that differs from congenital myopathies.

02:54 Myopathies are a problem where the muscle doesn't die, is dysfunctional, doesn't work right and patients are weak.

02:59 But there's not that progressive course that we see with muscular dystrophies.

03:03 And so those are two very important conditions that we need to consider on the differential for a floppy baby, as well as metabolic myopathies and then there are some other congenital myopathies that could be included.