Bilateral Lower Limb Spasticity
Bilateral lower limb spasticity is the most strongly supported diagnosis in this clinical scenario, as it represents the hallmark clinical manifestation of spastic diplegia cerebral palsy, which is defined by the functional outcome of scissoring gait and periventricular leukomalacia on MRI. 1
Why Bilateral Lower Limb Spasticity is the Correct Answer
The clinical syndrome of spastic diplegia cerebral palsy is specifically defined by bilateral lower limb spasticity as its functional outcome 1. This is not merely a symptom but the defining clinical diagnosis that captures the specific motor pattern seen in this child.
- Scissoring gait is pathognomonic for bilateral lower limb spasticity, where increased adductor tone causes the legs to cross over each other when the child is held upright 1
- Periventricular leukomalacia (PVL) is the anatomic substrate most strongly associated with spastic diplegia, as the periventricular white matter contains descending motor tracts to the lower extremities 2, 3
- The combination of scissoring and PVL on MRI makes bilateral lower limb spasticity the most specific and clinically relevant diagnosis 1
Why the Other Options Are Less Supported
Static Motor Delay (Option A)
While cerebral palsy is by definition a static encephalopathy with motor dysfunction, "static motor delay" is too vague and non-specific to capture the specific pattern of bilateral lower limb spasticity that defines this child's condition 1. This term fails to identify the characteristic bilateral lower extremity involvement.
Prematurity (Option C)
Prematurity is a risk factor, not a diagnosis 1. While 24 of 25 children with PVL in one study were preterm births 3, and PVL incidence is significantly higher in cases of prematurity 4, prematurity itself is not what the clinical presentation and MRI findings "support"—they support a specific neurological diagnosis.
Periventricular White Matter Changes on MRI (Option D)
This option confuses the imaging finding with the clinical diagnosis 1. The MRI finding of PVL should not be confused with the clinical diagnosis of bilateral lower limb spasticity, which is defined by the motor manifestation, not the radiographic appearance 1.
Clinical Correlation and Prognosis
- PVL is strongly associated with spastic diplegia, with 36% of children developing spastic diplegia and 48% developing quadriplegia in one cohort 3
- Motor outcomes correlate with PVL severity: Children with grade 2 or 3 PVL have significantly worse motor impairment and walking ability compared to grade 1 PVL 3, 4
- Mobility is significantly reduced in patients with PVL, with only 40% able to walk independently at 36 months even with bracing 3
- The rate of mobilization is significantly lower and epilepsy rates are significantly higher in patients with PVL 4
Critical Pitfall to Avoid
Do not mistake the radiographic finding (PVL) or the risk factor (prematurity) for the actual clinical diagnosis. The question asks what is "most strongly supported by the diagnosis"—meaning what clinical entity is being diagnosed based on the presentation and imaging. The answer is the specific motor pattern: bilateral lower limb spasticity, which defines spastic diplegia cerebral palsy 1.