Evaluation of the Hypotonic Infant

by Roy Strowd, MD

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    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.

    About the Lecture

    The lecture Evaluation of the Hypotonic Infant by Roy Strowd, MD is from the course Hereditary Neuromuscular Disorders.

    Included Quiz Questions

    1. Congenital muscular dystrophy would show muscle necrosis on biopsy.
    2. If the baby’s mother has myasthenia gravis, the baby’s prognosis is poor.
    3. Congenital myopathy would show muscle necrosis on biopsy.
    4. Metabolic disorders can be excluded because patients typically don’t become symptomatic this early.
    5. CNS abnormalities can be excluded because they cause hyperreflexia.

    Author of lecture Evaluation of the Hypotonic Infant

     Roy Strowd, MD

    Roy Strowd, MD

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