Spinal muscular atrophy (SMA) is a genetic neuromuscular disease that affects motor neurons in the spinal cord, leading to progressive muscle weakness. It has varying severity depending on the number of SMN2 genes. SMA is classified into 4 types based on age of onset and highest physical milestone achieved. Management is supportive and focuses on nutrition, pulmonary health, scoliosis, contractures and hip dislocation. The disease has no cure and treatment aims to prolong survival and maximize quality of life through multidisciplinary care.

1. Spinal muscle atrophy
Shady Mahmoud
Assistant lecturer
Orthopaedic surgery department - Ain Shams University

2.  A neuromuscular disease of infancy, childhood, and
adulthood, that effects the survival and function of the
anterior horn cells of the spinal cord.
 It is characterized by progressive, predominantly
proximal and symmetric muscle weakness.
 Sensation and cognition are preserved,
 It is one of the leading genetic causes of infant mortality,
with an incidence of 1 in 6,000 to 1 in 10,000 reported in
a European population.

3. Genetics
 A deletion of the telomeric gene survival motor neuron 1 (SMN1)
located on chromosome 5 (5q13) was found in 98.6% of patients
(AR disease)
 There are two copies of SMN genes (telomeric and centromeric)
that encodes neuronal apoptosis inhibitory protein.
Spinal muscular atrophy involves the telomeric one (SMN 1).
 The SMN protein is critical to RNA metabolism, and patients with
SMA have a shortage of SMN protein, leading to motor neuron
death.
 The severity of disease is mitigated by the number of copies of
SMN2 gene in each cell. Multiple copies of SMN2 gene allow for
production of SMN proteins, reducing disease severity, and allowing
the disease to present later in life.However, predicting SMA type
based on SMN2 levels is not recommended because of poor
correlation between genotype and phenotype.

4. Classification (based on age of onset)
Type Name Presentation prognosis
Type 1 Acute Werdnig-
Hoffman disease
 Present < 6 months
Classic floppy baby
 Poor head control, difficulty of swallowing and
feeding
 Tongue atrophy and fasciculations
 Limb and trunk hypotonia, absent deep tendon
reflexes, and intercostal muscle weakness
Poor, usually die by 2 yrs
Type 2 Chronic Werdnig-
Hoffman disease
 Present 6 -18 months
 Delayed motor milestones, the functional ability
to maintain a sitting position without support
 Scoliosis, joint contractures, and intercostal
muscle weakness
Expected to live into their
twenties and beyond
Type 3 Kugelberg-
Welander disease
 Present > 18 months
 Ambulant, hand tremors, muscle fasciculations
 Scoliosis, hip abductor weakness, resulting in
Trendelenburg gait or hip extensor weakness that
results in increased lumbar lordosis
Those who maintain
ambulation is not
markedly different from
that of the non SMA
population
Type 4  present in 2nd
- 3rd
decade
 mild motor impairment
As type 3

5. Clinically
It is a pure LMNL
Suspected in any child with hyotonia, areflexia, bilateral symmetrical
proximal weakness, and fasciculations
Main considerations:
1) Non orthopaedic:
a) Developmental delay
b) Gastroeneterology
c) Pulmonary
2) Orthopaedic:
a) Scoliosis
b) Contrctures
c) Hip disloction

6. Investigations Blood tests:
a) Targeted mutation analysis:
deletions of exon 7 and 8, SMN1 gene (95-98%)
SMN2 copy count
results of this blood tests are available in an average of 2 to 4 wks
b) Creatine kinase enzyme: normal
 Electrodiagnostic studies:
a) Motor nerve conduction study: abnormal
b) Sensory nerve conduction study: normal
c) EMG: denervation potentials
 Biopsy (rare):
a) skeletal muscle: atrophic fibres with islands of group hypertrophy,3
b) spinal cord: shows severe loss of motor neuron in the anterior horn
region

7. The spinal cord anterior horn region shows an absence of motor neurons in a patient (B)
compared with those in the healthy control (A).
Skeletal muscle of a patient (D) shows hypertrophic fibres (hollow arrowhead) surrounded
by group atrophy (green arrowhead) compared with healthy fibres with uniform
morphology in normal infantile muscle (C).

8. Developmental delay
 Intelligence is normal
 Gross motor milestones
SMA1: no significant milestones are achieved
SMA2 and 3: may lose mobility as they age
 Fine motor skills
Variable – based on upper extremity
involvement

9. Gastroeneterology
 Failure to thrive
Dysphagia: poor coordination of swallow and
airway closure
Chewing difficulties: masticators and facial
weakness
Fatigue: decreased efficiency of pre-oral, oral
and pharyngeal phases
 Gastroesophageal reflux:
Increased risk of aspiration

10. Pulmonary
 Major cause of morbidity and mortality in SMA 1
and 2.
 Risk factors:
 Weak inspiratory and expiratory muscles
 Scoliosis – older SMA 2 and 3
 Progressive restrictive lung disease
 Swallowing dysfunction and reflux
 Progression to respiratory failure via recurrent
infection and nocturnal desaturation and
hypoventilation

11. Management: mainly supportive
 Formal swallow evaluation (OPM)
 G-tube placement
 Dietary modifications
 Medication management for reflux
 School modifications to accommodate physical
disabilities
 PT/OT – functional skills
 Pulmonary evaluation every 6 months is
recommended

12. Scoliosis
 Prevalence of scoliosis in patients with
SMA ranges from 60% to 95% in several
series.
 patients with type 1 or 2 SMA have larger
spinal curves and more rapidly
progressive scoliosis.
 curves are typically right sided
thoracolumbar long and C-shaped.

13. AP (A) and lateral (B) radiographs of the spine demonstrating a
long, C-shaped thoracolumbar curve measuring 93° in a 12-
year-old girl with type 2 spinal muscular atrophy

14.  Non-operative:
a) Observation: for small curves
b) Bracing: for larger, progressive curves.
several series have reported that bracing is ineffective in
halting curve progression and may worsen the
respiratory function but it may provide limited sitting
support in those with collapsing curves.
The benefits of supported sitting must be weighed against the limitation
of chest wall excursion caused by bracing.
 Operative:
Surgery is indicated for progressive deformity in spite of
orthotics, and curves >70 degree
In children with a skeletal age ≤9 years a growing rod
anchored distally to the pelvis is preferred.
patients with open triradiate cartilage with skeletal age >10
years PSF with pedicle screws inserted at most levels
from T2 to the pelvis is done

15. AP (C) and lateral (D) radiographs demonstrating a thoracolumbar
curve of 10° following posterior spinal fusion from T2-S1 and pelvic
fixation with S2 alar iliac screws.

17. Contrctures
 Common in the hip and knee
 Treatment
Physical therapy.
Surgical release: controversial as the function in non-
walkers is rarely improved and recurrence is common.

18. Hip disloction Ambulatory patients with the mild form of SMA have a better chance
of maintaining a concentric hip than do those with severe or
intermediate forms.
 Hip pathology may be caused by muscle weakness, imbalance, and
pelvic obliquity.
 In general, attempts to reduce the hip surgically in patients with
SMA have been unsuccessful (high recurrence rate if open
reduction attempted).
 Many theoretical concerns regarding maintenance of a non-
concentric hip, including problems with sitting imbalance, difficulty
with perineal care, and pain with hip range of motion relate to
spastic hip and have not been found in neuromuscular disorders
presenting with low tone, such as SMA.
 However, further research is required to determine whether hip
dislocation in patients with SMA can be tolerated over the entire
lifespan or not.

20. THANK YOU