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Weakness, Hypotonia, and the Floppy Infant

So what are the manifestations of weakness in infants? Paucity of movement, feeble cry, weak suck, hypotonia, delayed motor milestones as the baby grows. The baby may look like this. This is an example of a floppy infant. Normal babies, if you hold them like this, would actually have some neck extension and would bring their legs up, and their back would not be like a completely inverted U. So this baby has spinal muscular atrophy, also known as Werdnig-Hoffman syndrome. Here’s another baby. This is what we call "severe head lag". So again, another manifestation of floppiness. In older children there may be persistent lordosis as they walk, that may signal something. Shoulders may be droopy. The arm swing may be diminished when they walk.

The onset and cause are important to neurologists because some kind of weaknesses may be very very acute. They may not be neuromuscular at all. It may have been a stroke. So strokes are very very abrupt in onset, as is head trauma. Sub-acute processes would be inflammatory’s, somebody with myositis. Or it may be cerebral vasculitis with lupus. There are also diseases that are insidious, degenerative disease, metabolic disease. And then we also have diseases that are intermittent. There are diseases where the symptoms come on, they remit and then they may come on again. And that’s the periodic paralysis where it may be episodic truly. In myasthenia gravis it is fluctuating.

Werdnig-Hoffman type I is what we call those infants that you saw some pictures of, that are really floppy at birth, cannot feed, have respiratory problems and a lot of them end up dying, unable to breathe, in the very first year. Type II was the one that presented a little later and some of the type II’s may last into the second decade. Kugelberg-Welander is again the same disease. It is just much milder and may in fact present as late as the second decade. One of the interesting things about the Werdnig-Hoffman babies that is heartbreaking is that the cranial nerve muscles, bulbar muscles as we call them, are spared until the end so they have respiratory problem and yet they can move well, their eyes look very bright, they have normal extraocular movements, but their brain is completely uninvolved.

I’m showing you just this slide to show you what happens. You know, sooner or later everyone will confess that they get very confused. What is all this spinal muscular atrophy inducing muscular dystrophy, right? Well, what’s the difference. Well when the problem is in the neuron and not on the nerve and not on the muscle, the nervous system is trophic to the muscle. So when a motor neuron dies all the bundles that are enervated undergo atrophy. In muscular atrophy you get this grouped atrophy because each time a motor neuron dies the neighboring twigs sprout. So increasingly, the neighboring ones become the same, type I or type II, and then when that motor neuron that earlier sprouted begins to die, now you have a whole geographic region that’s atrophying and looking small right.

Dejerine-Sottas is a demyelinating neuropathy but it occurs actually in infancy. Kids will have very high spinal fluid proteins, motor milestones are delayed, and unlike Charcot-Marie-Tooth, Dejerine-Sottas is a very very severe condition. Dejerine-Sottas will severely impair a patient. Charcot-Marie-Tooth, the prognosis is not so bad. There are many people who grow well into adulthood, get married, have children.

Here is the distal atrophy of Charcot-Marie-Tooth again. You saw this picture earlier. There are other peripheral neuropathies that may be highly focal in nature. You should know a little bit about Bell’s palsy. I’m not going to go through the details. This is just a reminder for you to develop your list. As you know, Bell’s palsy is a peripheral VII nerve, often post infectious, often related one of the herpes viruses.

There are infectious neuropathies. Obviously a popular item today is Lyme disease. It’s again, the associations you make are tick bite, migrating rash, deer hunting in Connecticut. From a neurologists point of view, multiple cranial neuropathies are often the presentation of the neurologic syndrome. You know antibiotic treatment early can be instituted and it is entirely conceivable that a vaccine is now becoming available for Lyme disease. Diphtheria can cause a significant neuropathy. The association for diphtheria, which again we do not see very often, is dysphagia, dysphonia and extraocular muscle involvement along with, again that word, loss of reflexes. So that’s diphtheria. Mainly a Board-type of entity rather than reality. Leprosy; again we don’t see that very often unless you have traveled in Asia or Africa, but in the third world is it a very big problem still. It’s a microbacterium that causes a very profound peripheral neuropathy.

Post-infectious polyneuropathies. There is Guillain-Barre, Landry’s and there is symmetric ascending - so anytime you see a neuropathy, a weakness that starts bilaterally, starts in the lower extremity, progresses to upper extremity, you have to think about this. Calf pain can be the earliest complaint occasionally in kids. The other buzz word is these people have no pleocytosis but increased protein.

Traumatic neuropathies. These are again quick bullet points. We don’t need to really know extensive details of these but you need to be able to associate that Erb’s is a brachial nerve palsy. It’s there in your Neonatology section. Shoulder dystocia and traction injury, and they present with either upper or lower. They are called "Erb’s versus Klumpke." Occasionally if the OB has been particularly violent.

Toxic neuropathies. Lead, we told you about that wrist drop. There it is. Asymmetric neuropathy with wrist drop, there may be anemia, GI discomfort but most of the young kids we see with lead toxicity come with encephalopathy, learning disabilities. There may be a history of pica. Lead levels may be high. Mercury, we don’t need to talk about. Rather rare but again it’s one of those things. Boards like you to know a little toxicology. It may be a neuropathy associated with tremor and ataxia.

Myasthenic syndromes. So there may be neonatal myasthenia where maternal IgG is transferred. The baby presents with ptosis, feeble cry, faltering, but basically a floppy infant but you have the history that mother has myasthenia and it will resolve over a few weeks. It’s really mothers IgG. Congenital is a familial disease, often mild. The juvenile myasthenia gravis is similar to the adult disease.

Infant botulism is the next condition. That’s also a neuromuscular disease. Here is the association. Spores of the clostridial toxin. The toxin comes from the organism, but the baby ingested the organism spore, not the toxin itself. It’s the gradual onset of hypertonia, ptosis.

Becker-induced dystrophies, facioscapulohumeral and limb-girdle dystrophies, congenital myotonic dystrophy, congenital muscular dystrophies, congenital myopathies, the myocitides and metabolic muscle disease. So we’ll very quickly run through a bunch of these and Becker and Duchenne are both x-linked, both are coming out of the same gene. It is a gene product that is called dystrophin. It’s a membrane-associated protein. These are kids who are not floppy babies as newborns. They are entirely normal.

Fascioscapulohumeral or limb-girdle or focal muscular dystrophies. They are usually later in onset with mild progression. One is dominant, the other is recessive. Biopsy will show mildly dystrophic changes. The life-span is generally normal but they may need some assistance.

Congenital myotonic dystrophy is an important recognition. It’s a dominant disease with what is emerging as a big picture now. It is a disease which passes on generation to generation, particularly if it is maternally passed on it will be much more severe in the baby.

Congenital muscular dystrophies. Now let us flash back and say that’s congenital. What’s the word? Myotonic. Not to be confused with muscular. These are heterogenous groups often presenting in the neonatal period with floppiness and arthrogryposis. Some of them may have brain involvement with seizures and mental retardation. And again, here’s the other important distinction. The biopsy looks dystrophic, which you already know. The reason we keep showing you those biopsies is so you don’t confuse congenital muscular dystrophy.

Metabolic muscle disease. You should know a little bit about Pompe’s, the genetics people will tell you about. Most of these kids present with cardiomyopathy. It’s a glycogen storage disease presenting with severe cardiac and skeletal muscle involvement. There is McArdle’s which onsets in the second disease, another glycogen storage disease. Glycogenopathy. Here you have … it’s myophosphorylase deficiency actually. Usually this will be young adolescent presenting with difficulty running or playing basketball, or they get cramps.

There is a lipid myopathy. Lots of lipid that the muscle is not able to utilize. Periodic paralyses, are popular items. There are two of them. Both are autosomal dominant, both of them can be treated with acetazolamide. One type is the hyperkalemic with high potassium, so it’s early childhood onset. It’s precipitated by rest and the attacks are brief. I have underlined things you should remember. In your handout as well. Hypokalemic is later in onset and lasts longer. That’s how you remember that. And hypokalemic is provoked by carbohydrate load. You can kind of make sense out of it; if you ate a lot of carbohydrates maybe insulin goes up, and you know that association of insulin and potassium loads.