disease or spinal muscular atrophy type I is an autosomal recessive disorder
caused by premature death of the alpha motor neurons. A history of decreased
and weak fetal movements in the last trimester is often present. Neonates
with Werdnig-Hoffmann disease may have different presentations: (1) hypotonia
from birth, (2) an acute onset of hypotonia and weakness after an apparently
normal period, or (3) acute onset of respiratory failure.
Hypotonia from birth is the most common presentation.
Werdnig-Hoffmann disease usually
presents with hypotonia and decreased dynamic tone. Hypotonia and decreased
dynamic tone affects the axial musculature more than the appendicular
musculature, the proximal muscles more than the distal muscles, the lower
extremities more than the upper extremities, the lower cranial nerve muscles
more than the upper cranial nerve muscles, and, in most cases, the intercostal
muscles more than the diaphragm.
The tongue of a neonate with
Werdnig-Hoffmann disease may be weak, thin, and have clinical fasciculations.
Fine rhythmic tremor of the finger may be present (polyminimyoclonus).
Neonates with Werdnig-Hoffmann disease look alert. They do not have ptosis,
ophthalmoplegia, or sphincter or sensory disturbances. Serum creatine
phosphokinase, sensory nerve conduction, and motor nerve conduction in
the neonatal period are normal.