Neuromuscular Junction Disorders
Specialist in Pediatric Neurology & Developmental Pediatrics
İstanbul University-Cerrahpaşa Faculty of Medicine · Nörogender Association
Last reviewed:
Intended for healthcare professionals
The common signature of junction disorders is fatigability with oculobulbar involvement: ptosis, ophthalmoplegia, swallowing difficulty, fatigue on chewing, deterioration of speech; worsening as the day goes on and improvement with rest.
Congenital myasthenic syndromes
These are inherited disorders due to mutations in genes encoding presynaptic, synaptic or postsynaptic components of the junction. Onset is at birth or in infancy. They are not autoimmune and antibodies are negative.
- Ptosis and ophthalmoplegia from birth, with sucking and swallowing difficulty.
- Recurrent, unexplained apnoeic episodes, particularly during febrile illness.
- Deterioration later in the day, a weakening cry.
- Arthrogryposis may be present.
Acetylcholinesterase inhibitors give clear benefit in some subtypes, but in others (for example slow-channel syndrome and COLQ-related syndromes) pyridostigmine makes the picture worse. Long-term treatment should therefore not be decided before the genetic subtype is established. Salbutamol, ephedrine, 3,4-diaminopyridine and, in slow-channel syndrome, fluoxetine or quinidine are other agents used according to subtype.
Juvenile myasthenia gravis
This is autoimmune; acetylcholine receptor or MuSK antibodies may be detected. Two clinical forms are seen in childhood: a purely ocular form and a generalised form. Diagnosis rests on antibody testing, repetitive nerve stimulation and clinical response. Treatment includes pyridostigmine, corticosteroids, steroid-sparing immunosuppressants and, in severe cases, intravenous immunoglobulin and plasma exchange. Myasthenic crisis is an emergency presenting with respiratory failure.
Aminoglycosides, fluoroquinolones, macrolides, magnesium and some cardiac drugs aggravate the condition; this list should be kept in the patient's notes.
Infant botulism
An acquired junction disorder and part of the differential diagnosis of acute hypotonia. Constipation is usually the first sign, followed by feeding difficulty, a weak cry, ptosis, ophthalmoplegia, a dilated pupil with a sluggish light response and descending symmetrical weakness. Honey consumption should be asked about, although in most cases the source is environmental dust. Diagnosis is by stool toxin analysis; treatment is botulism immune globulin and supportive care.
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