(Infantile or type I spinal muscular atrophy)

Neurologic disease causing muscle atrophy due to the degeneration of spinal motoneurons. Autosomal recessive transmission of a mutation of the SMN1 gene(5q11.2-q13.3), responsible for the synthesis of protein essential for the survival of the spinal motoneurons. It is the most severe form of the disease (see Spinal amyotrophias): by definition, the disease begins before 6 months of age and these children do not acquire the ability to sit without help.

Three types have been identified:

-        type 1A: first clinical signs before 15 days of life: severe motor involvement with swallowing difficulties and respiratory distress

-        type 1B: first clinical signs before 3 months of age, no acquisition of head control

-        type 1C (or 1bis): first clinical signs between 3 and 6 months of age, acquisition of head control

First manifestations in the first 6 months of life:

-        hypotonia with symmetric and rapidly progressive paralysis of the roots of the 4 limbs (amphibian position)

-        thoraco-abdominal swing because the intercostals muscles are involved before the diaphragm (bell-shaped chest)

-        pathognomonic presence of lingual fasciculations and sometimes tremor of the extremities (30 %)

-        major respiratory failure

-        sharp gaze (normal intelligence)

-        sometimes associated cardiac abnormality: ASD, VSD, hypoplasia of the left ventricle

-        death usually before 2 years of age

Treatment:

• tracheostomy and artificial ventilation
• prevention of respiratory infections: physiotherapy
• nasogastric tube feeding or gastrostomy
• experimental treatment: intrathecal nusinersen  therapy

Anesthetic implications:

echocardiography; gastrostomy feeding. Midface hypoplasia following the use of non-invasive ventilation with a face mask. Tracheotomy. Risk of sudden death. Locoregional anesthesia has been successfully used. No succinylcholine: risk of hyperkalemia. Difficult monitoring of the neuromuscular function.

Intrathecal administration of nusinersen allows to recover some motor skills and improves the quality of life. Risk of hepatotoxicity in case of gene therapy with onasemnogene abeparvovec.

References : 

• Stucke A, Stuth EA. 
  Use of rapacuronium in a child with spinal muscular atrophy. 
  Paediatr Anaesth 2001; 11: 725-8.
• Durkin ET, Schroth MK, Helin M, Shaaban AF.
  Early laparoscopic fundoplication and gastrostomy in infants with spinal muscular atrophy type I.
  J Pediatr Surg 2008; 43: 2031-7.
• Wilton NCT.
  Spinal muscular atrophy : the challenges of “doing the right thing ».
  Pediatr Anesth 2009; 19: 1041-7
• Brown AF, Einhorn LM.
  Anesthesia in a child with advanced Spinal Muscular Atrophy type 1 receiving maintenance nusinersen therapy : a case report.
  A&A Practice 2020 ; 14 e01206
• Audic F, Barnerias C.
  Spinal muscular atrophy (SMA) type I (Werdnig-Hoffmann disease).
  Arch Pédiatr 2020; 27: S15-17

Update June 2020