Neuromuscular disorders in children

A change in the SMN1 gene causes the motor nerve cells in the spinal cord to be lost. According to a literature review and international standards, it affects roughly 1 in every 10,000–11,000 live births, and the most severe form (type 1) accounts for about 60% of cases. Type 1 begins in the first months of life: the baby moves the legs very little, cannot hold the head up, sucks weakly, the tongue twitches, the baby breathes with the belly and has a weak cry; reflexes are absent. In type 2 a child can sit but does not walk; in type 3 a child walks, but the weakness gradually increases.

The diagnosis is made by genetic testing (SMN1 deletion) and should not be delayed in a baby with suspected SMA. Treatment includes an antisense drug (given into the spinal canal), gene therapy (a one-time intravenous infusion) and an oral drug, and all of them change the course of the disease. In a randomized trial, 51% of the treated babies reached milestones such as head control, rolling and sitting, compared with none in the control group; the risk of death or permanent ventilation was also significantly lower. For this reason, some countries have added SMA to newborn screening. Alongside treatment, international standards call for planned physical therapy, orthopedic monitoring (curvature of the spine, the hip joint), nutrition and breathing support. SMA: early signs and treatment

Inherited neuropathies (Charcot-Marie-Tooth): the most common inherited nerve disease; in population studies the prevalence ranges from 10 to 80 per 100,000 people, depending on the country. Signs include gradually increasing weakness and thinning in the legs and hands, a high arch of the foot, foot drop, frequent falls and reduced sensation. The diagnosis is made with EMG/nerve conduction studies and genetic testing; treatment is physical therapy, orthoses and orthopedic follow-up.

Guillain-Barré syndrome: an acute, immune-mediated neuropathy. It usually begins 1–3 weeks after an infection, with weakness that starts in the legs and climbs upward, refusal to walk, pain and loss of reflexes; the breathing muscles and swallowing may be affected. This is an emergency: the child is monitored in the hospital and treated with immunoglobulin, and the great majority of children recover fully.

Other causes: vitamin B12 deficiency, diabetes, some medications, poisonings.

Juvenile myasthenia gravis: the immune system damages the receptors that pass the signal from nerve to muscle. The hallmark is weakness that increases through the day and eases with rest: drooping eyelids toward evening, double vision, tiring when chewing and swallowing, a hoarse voice. The diagnosis is made with an antibody test and special electrophysiological tests; treatment is symptomatic drugs, immune treatment and, in selected cases, removal of the thymus gland. In a child with a drooping eyelid or crossed eyes, monitoring vision ("lazy eye") is important. Transient myasthenia in a newborn (from the mother's antibodies) is a separate condition and resolves in a few weeks.

• Neurological exam: distribution of weakness, muscle bulk, reflexes, sensation, tongue twitching, eyelids, fatigue tests
• EMG/nerve conduction studies: nerve conduction and muscle activity; they tell nerve, muscle and junction diseases apart
• Genetic testing: SMN1, Charcot-Marie-Tooth genes and others
• Blood tests: CK, antibodies (myasthenia), B12, thyroid
• Spinal fluid analysis and MRI in Guillain-Barré and other acute cases
• Assessment of breathing function and swallowing