A case of a misdiagnosed child with R-CMAP, medical micro-theory, season 4

"Dr.
Diaosi Wang Xiaopeng" series of novels have a lot of professional knowledge, each chapter is a case, there are difficult cases, and there are ordinary cases
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The purpose of this book is to hope that you can read leisurely and relax after busy work.
If you can inspire your profession, it will be great
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Author: Wang Mingyue This article is published by Yimaitong authorized by the author, please do not reprint without authorization
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Chapter Nineteen: R-CMAP This chapter starts with the concept again, because many concepts are not studied deeply, which leads to a very superficial understanding of certain diseases, and it is easy to be tricky and unable to judge well when you see a case
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 What is R-CMAP? CMAP is a compound muscle action potential, and R is Repeat, which literally means two CMAPs appear
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(See the figure below) From the figure, we can see the independent M2 wave after the main wave M1
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 That is, when we stimulate the median nerve, ulnar nerve, tibial nerve.
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two CMAPs will appear.
Why? The reason is that there is more acetylcholine in neuromuscular junctions, such as organophosphate poisoning, such as overdose of brompistigmine tablets
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Organophosphorus is a refractory anticholinesterase drug, and brompistigmine tablets are a reversible anticholinesterase drug.
The effects of the two are similar, but the degree is different
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 If you understand this truth, you will know: If R-CMAP occurs in nerve conduction, it is absolutely impossible to use brompistine tablets, because this will undoubtedly add fuel to the fire and worsen the situation
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 Today's case is a child who was misdiagnosed as MG
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 One day, Bai Jiao received an 11-year-old boy in the outpatient clinic.
The child's exercise ability was weaker than his peers since childhood, and he was more prone to fatigue under the same intensity of exercise
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The child’s symptoms gradually worsened.
When he came to see the doctor, he could see mild weakness in his limbs lifted up, and there would be obvious fatigue after mild exercise.
After a short trot, it would be difficult to stand up, and he would get better after a rest.
Suspicious mornings and evenings.
There is no sensory disturbance
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 The child’s medical history makes it easy to think of myasthenia gravis.
The outside hospital was also diagnosed with MG, and the outside hospital’s RNS test showed that the amplitude decreased by 15% under clear low-frequency stimulation
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 The recurrence was positive and the symptoms were relatively typical.
Bai Jiao still admitted him to the ward with MG
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 The patient’s muscle enzymes were normal, and no myogenic or neurogenic damage was seen on the EMG.
The results of acetylcholine receptor antibody and MuSK antibody were not returned.
After admission, the patient was given brompistigmine tablets 30 mg tid empirically.
Surprisingly, The child’s symptoms worsened progressively, with drooping eyelids and dyspnea.
Bai Jiao suspected a cholinergic crisis.
Bropistigmine tablets were stopped and IVIG 15g/d*5 days later, the symptoms resolved
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 I thought it would end there, and planned to go home to take hormones and MMF
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 Before he was discharged from the hospital, Wang Xiaopeng made routine rounds and unexpectedly learned that the child had a history of asthma and would take salbutamol during the attack
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 "Do you think that during an asthma attack, the child's weakness symptoms will get better?" Wang Xiaopeng asked
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 "It seems that this is the case
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" The mother of the child replied
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 "Bai Jiao, the child takes brompismine tablets and the symptoms worsen, but the β2 receptor agonist is effective.
It may be congenital myasthenia syndrome.
Then review an electromyogram to see if there is R-CMAP.
CMS-related genetic testing
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Parents also make one together
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"Wang Xiaopeng said to Bai Jiao
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 Sure enough, R-CMAP on nerve conduction and missense mutations in the COLQ gene were found .
After terbutaline 2.
5 mg bid was given, the patient's activity endurance was significantly better than before
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 Knowledge points CMS is a rare nerve.
Muscle junction diseases are mostly inherited in autosomal recessive mode.
Only slow channel syndrome is inherited in autosomal dominant mode
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According to its damage site, it can be divided into presynaptic defects, synaptic defects, and postsynaptic defects.
The molecular mechanism is different, and it can be divided into many subtypes
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 Among the mutant genes discovered, CHRNE gene mutation is the most common and the first mutant gene to be discovered
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This gene mutation can cause acetylcholinesterase deficiency, which is synaptic The most common form of CMS is autosomal recessive inheritance, mostly homozygous mutations or compound heterozygous mutations
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There is no clear correlation between COLQ gene mutation types and phenotypes, additional modifiers or environmental factors may exist Participating in it, previous reports have mentioned that heterozygous carriers may have mild weakness such as congenital ptosis and electromyographic changes, suggesting that COLQ gene carriers may have symptoms of muscle weakness
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 Common clinical features of CMS: 1.
Onset is early, more often than in infancy or at birth; 2.
Muscles are easily fatigued, with fluctuating symptoms; 3.
Extremity weakness, feeding difficulties, breathing difficulties and other manifestations occur frequently; 4.
Myopathy-like manifestations such as muscles Atrophy; 5.
Myasthenia gravis-related antibodies are negative
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 Some special clinical symptoms may indicate a certain disease or a gene defect, such as slow channel syndrome, acetylcholinesterase deficiency, poor application of cholinesterase inhibitors, but A characteristic R-CMAP wave appears
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 In terms of treatment, the treatment response of patients depends on different subtypes.
Except for slow channel syndrome, acetylcholinesterase deficiency, DOK7 deficiency, LAMB2 deficiency, brompistigmine can be used for the other first-line treatments
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At the same time CMS can benefit from β receptor agonists
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