Clinical History
- Patient is a 3-month-old girl born at 37.5 week, and born hypotonic with minimal movements and some hand contractures at birth, areflexic, but no tongue fasciculations. Subsequently developed twitching in tongue muscles in her tongue. At 3 months, infant had a tracheostomy and was ventilator dependent with normal head growth and gastrostomy tube for dysphagia.
- Physical exam: dysphasia with coughing and choking; extremity weakness and toe fasciculations.
- MRI of brain was normal.
What is the most likely diagnosis? (Reference images below)
A.) Congenital myopathy
B.) Type 1 fiber predominance
C.) Spinal muscular atrophy
D.) Duchenne muscular dystrophy
Correct Answer: C. Spinal muscular atrophy (SMA)
Final findings and diagnoses:
Patient genetics: heterozygous missense mutations inSMN1
Phenotype: types defined by age at onset
- Very severe infantile (0-6 months) type I, Werdnig-Hoffman disease
- Intermediate (6-18 months) type II; Dubowitz disease)
- Juvenile (>12 months) type III; Kugelberg-Welanderdisease
- Adult onset (adulthood) type IV
Genetics: Autosomal recessive; 1:10,000 live births (US); usually involves SMN1 gene with SMN2 as disease modifying gene.
Histology: varies with type; severe type II fiber atrophy with rare type I hypertrophy is compatible with severe infantile form (SMA I) seen in this case.
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