1.1

Introduction

Muscle tone changes progressively over the very first months of life and is a key factor for postural learning, such as holding the head up between eight and 12 weeks, maintaining a sitting position without help at nine months, standing at 10 months and so on. Indeed, muscle tone maturation continues until the age of 24 months . During this period, hypotonia may be the only symptom of a central or peripheral nervous system disorder . In 66 to 88% of the cases, neonatal hypotonia has a central origin .

Electroneuromyography (ENMG) is known to provide useful information on many neuromuscular diseases. We propose to assess the sensitivity of ENMG in the aetiological diagnosis of hypotonia of peripheral (for example, neuromuscular) origin in infants and toddlers.

1.2

Patients and methods

This is a retrospective, single-centre study in a neuropediatrics department. The study population concerned children aged between zero and 24 months, who underwent an ENMG in the etiological approach of their hypotonia and whose final diagnosis was a clearly defined neuromuscular disease, between 1994 and 2006. ENMG included studies of motor conduction velocity on the tibial nerve, sensory conduction velocity on the median nerve, an electromyography on gluteus maximus , tibialis anterior and biceps brachii for muscle contraction and quadriceps for spontaneous activity at rest.

Slowed nerve conduction velocity to half the normal rate or less leads to the diagnosis of demyelinating neuropathy. A denervation pattern is very suggestive of a spinal muscular atrophy: large amplitude, long duration, and polyphasic individual motor unit potentials; fasciculations; fibrillations and positive sharp waves. A myopathic pattern is evocative of a muscle disease, inherited in most of cases: low amplitude, polyphasic and short duration motor unit potentials.

We compared the electromyographic data with the current diagnosis determined by muscle biopsy and/or specific gene studies.

The study population included 37 children (19 girls, 18 boys): 16 had various congenital myopathies (diagnosed on the basis of a muscle biopsy referred to clinical data), 11 had typical spinal muscular atrophy (proven by homozygous deletion of exon 7 of SMN1 gene), five had muscular dystrophies (diagnosed on muscle biopsy), two had Steinert muscular dystrophy (proven by mutation in the DM1 gene), one had Charcot Marie-Tooth disease type IA (proven by duplication of the PMP22 gene), one suffered from Schwartz Jampel syndrome (proven by gene study) and one had atypical spinal scapulo-peroneal muscular atrophy (neurogenic ENMG, neurogenic pattern on muscle biopsy with suggestive clinical presentation).

At the time of the EMG assessment, the mean patient age was 164.5 days (range = 4 days to 2 years).

1.3

Results

Table 1 shows the ENMG results compared to the final diagnosis. All patients with spinal muscular atrophy or Charcot Marie-Tooth disease displayed neurogenic alterations on the EMG.

Among the 24 children ultimately diagnosed with myopathies, five only displayed myogenic alterations when tested before the age of two. Sixteen had normal EMG results and three showed neurogenic alterations; Table 2 shows the diagnostic data for these individuals.

1.4

Discussion

ENMG is not systematically performed in infants or young children with hypotonia. Arguments for a neuromuscular origin are needed:

• •
  

  lack of psychomotor delay (except for motor milestones);

  
  
• •
  

  lack of sensory impairment;

  
  
• •
  

  absence of pyramidal spasticity, dystonia, and cerebellar signs;

  
  
• •
  

  absence of deep tendon reflexes;

  
  
• •
  

  normal head circumference;

  
  
• •
  

  convincing weakness.

ENMG is a reliable ancillary test for the diagnosis of a spinal muscular atrophy (neurogenic muscle potentials, normal motor nerve conduction velocities) and demyelinating peripheral neuropathies (neurogenic muscle potentials, reduced motor and sensory nerve conduction velocities). In the diagnosis of spinal muscular atrophy, when clinical characteristics are clearly identifiable (proximal hypotonia and weakness, absence of deep tendon reflexes) the first diagnostic test should be the SMN1 gene deletion test (research of homozygous deletion of the exon 7). In some cases, geneticians may ask for a neurophysiological diagnosis confirmation before the SMN1 gene study.

Although myopathic ENMG alterations are described in review articles , normal ENMG seems more frequent in our study. Our findings are in accordance with the five previous retrospective studies in the literature ( Table 3 ). Three studies evaluated the diagnostic value of ENMG in hypotonia in children under the age of one and showed good agreement between EMG data and the final diagnosis in 90 to 100% of the cases with neuronal diseases but only 10 to 50% of the cases with muscle diseases . Rabie et al. compared the accuracy of EMG/nerve conduction studies with muscle biopsy and final clinical diagnoses in 27 children (aged from six days to 16 years); ENMG sensitivity for detecting myopathic motor unit potentials in myopathies was only valid in one of seven cases (14%) under two years of age but was far higher in older children (three out of four, 75%). In their series, ENMGs false-negative for myopathy in infants less than two years of age were neurogenic in three children (50%).

Electromyography (EMG) in infants differs from use of the method in older children or adults. It is not possible to interpret motor unit recruitment and, thus, a potential disproportion between the motor unit number and the effort output, which may be the only alteration in many myopathies. Another difficulty is that in infants, the normal characteristics of motor unit potentials may be very similar to those found in muscle diseases. Furthermore, many muscle diseases do not lead to alterations in the electrical signal; EMG can only authenticate myopathies which feature membrane dysfunction. Indeed, most congenital myopathies have a normal ENMG profile. Congenital muscular dystrophy could also be more prone to induce myopathic activity on needle EMG than non-dystrophic lesions .

The potential for neurogenic alteration in muscular diseases has already been described . It was observed in our series for two children with a multicore myopathy. Although a neuropathic EMG is classically considered as an exclusion criterion for multiminicore disease, some authors allow that “the clinical, pathologic and genetic overlap with congenital muscular dystrophy, with rigid spine syndrome will likely result in a reassessment of the nosologic boundaries between multiminicore disease and congenital muscular dystrophy” . In patient 13 ( Table 2 ), despite a neurogenic ENMG profile, we were able to advance several arguments for congenital muscular dystrophy: facial dysmorphia, arthrogryposis, major endomysial fibrosis in the absence of necrosis/regeneration in muscular biopsies, abnormal MRI results (polymicrogyria-like cortical gyration disorders in the sylvian fissures and vermian hypoplasia). Several authors found peripheral nerve involvement in congenital muscular dystrophy, especially in primary merosin deficiency . However, as emphasized by Quijano-Roy et al., a demyelinating peripheral neuropathy may be found in a merosine positive congenital muscular dystrophy . We performed a study of NCV measure in three cases of our five congenital muscular dystrophies and we never found any demyelinating neuropathy.

Advanced cases of nemaline myopathy may also have neurogenic alterations on ENMG .

1.5

Conclusion

In infants presenting with hypotonia, ENMG is useful for the diagnosis of peripheral neuropathy. Normal ENMG is relatively common for confirmed muscle disorders in infants whereas myogenic alterations seem more unusual, so that muscle biopsy appears unquestionable. In a few cases, early onset myopathies may present with a neurogenic ENMG pattern. Such a result should not invalidate the clinically presumed diagnosis of myopathy and would indicate on the contrary the need for a muscle biopsy.

2.1

Introduction

Le tonus musculaire évolue pendant les premiers mois de la vie et c’est un facteur clé pour les acquisitions posturales comme tenir la tête entre huit et 12 semaines, maintenir une position assise sans aide à neuf mois, se tenir debout à dix mois, etc. En fait, le tonus musculaire poursuit sa maturation jusque l’âge de 24 mois . Pendant cette période, l’hypotonie peut être le seul symptôme d’une maladie du système nerveux central ou périphérique . Dans 66 à 88 % des cas, l’hypotonie néonatale a une origine centrale . L’électroneuromyographie (ENMG) est réputée fournir des informations utiles sur de nombreuses maladies neuromusculaires. Nous nous sommes proposés d’évaluer la sensibilité de l’ENMG dans le diagnostic étiologique des hypotonies d’origine périphérique chez les nourrissons.

2.2

Matériel et méthode

Il s’agit d’une étude rétrospective, monocentrique, à partir d’un service de neuropédiatrie. La population étudiée était constituée d’enfants de zéro à 24 mois qui ont bénéficié d’un ENMG dans le cadre du bilan étiologique de leur hypotonie et pour qui le diagnostic final était clairement établi comme une maladie neuromusculaire, entre 1994 et 2006. L’ENMG comprenait une étude de la vitesse de conduction motrice du nerf tibial, une vitesse de conduction sensitive du nerf médian, une électromyographie du grand fessier, du tibial antérieur, du biceps brachial, pour l’étude des contractions musculaires et du quadriceps pour une recherche d’activité spontanée au repos. Un ralentissement de la vitesse de conduction d’au moins la moitié de la normale conduisait à un diagnostic de neuropathie démyélinisante. Des signes de dénervation suggéraient fortement une amyotrophie spinale (grande amplitude, longue durée et potentiel d’unité motrice polyphasique, fasciculation, fibrillation et onde pointue et positive). Un aspect myopathique était évocateur d’une maladie neuromusculaire héréditaire dans la plupart des cas (faible amplitude, potentiel d’unité motrice polyphasique et de courte durée).

Nous avons comparé les données électroneuromyographiques avec le diagnostic déterminé par la biopsie musculaire et/ou l’étude génétique spécifique.

Notre population est de 37 enfants (19 filles, 18 garçons) : 16 avaient une myopathie congénitale (diagnostiquée sur la biopsie musculaire en fonction des données cliniques), 11 avaient une amyotrophie spinale typique (prouvée par la délétion homozygote de l’exon 7 du gène SMN1 ), cinq présentaient une dystrophie musculaire (diagnostiquée sur la biopsie musculaire), deux avaient une dystrophie musculaire de Steinert (prouvée par la mutation du gène DM1 ), un avait une maladie Charcot Marie-Tooth de type 1A (prouvée par la duplication du gène PMP22 ), un souffrait d’un syndrome de Schwartz Jampel (prouvé par l’étude génétique) et un avait une amyotrophie spinale de type scapulopéronière (ENMG neurogène, aspect d’atteinte neurogène à la biopsie musculaire et présentation clinique évocatrice).

Au moment de l’ENMG, l’âge moyen des patients était de 164,5 jours (de quatre jours à deux ans).

2.3

Résultats

Le Tableau 1 montre les résultats ENMG comparés au diagnostic final. Tous les patients avec une amyotrophie spinale ou une maladie de Charcot Marie-Tooth présentaient des anomalies neurogènes à l’électromyogramme.

Tableau 1

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

Quelle place pour l’éducation thérapeutique des patients (ETP) en médecine physique et réadaptation (MPR) ? Contraception and screening for cervical and breast cancer in neuromuscular disease: A retrospective study of 50 patients monitored at a clinical reference centre Electronic tracking system and wandering in Alzheimer’s disease: A case study Chronic neck pain and vertigo: Is a true balance disorder present? Oncology and physical medicine and rehabilitation Total knee arthroplasty in a spinal cord-injured patient: A case report

Stay updated, free articles. Join our Telegram channel

Join