What is the most appropriate initial test to determine the cause of a child's gait problem, learning disability, and abdominal cramps?

Lead Poisoning is the Most Likely Cause of the Child's Symptoms

A blood smear is the most appropriate initial test to determine the cause of this child's gait problem, learning disability, and abdominal cramps, as it can reveal basophilic stippling characteristic of lead poisoning.

Clinical Presentation Analysis

The 7-year-old child presents with a constellation of symptoms highly suspicious for lead poisoning:

• Gait problem (neurological manifestation)
• Severe learning disability (neurocognitive manifestation)
• Recurrent abdominal cramps (gastrointestinal manifestation)
• Temporal relationship with moving into a new house (environmental exposure)
• Poor attention span (neurobehavioral manifestation)

This clinical picture strongly suggests lead poisoning, which is a common environmental toxin affecting children, particularly in older homes with lead-based paint.

Diagnostic Approach

Blood Smear (Option B)

• A blood smear is the most appropriate initial test as it can reveal basophilic stippling of red blood cells, which is characteristic of lead poisoning 1
• Lead poisoning causes inhibition of several enzymes involved in heme synthesis, resulting in anemia with distinctive morphological changes visible on peripheral blood smear
• The blood smear can also help rule out other causes of anemia that might present with similar symptoms

Other Options Analysis

1. Ultrasound of scrotum (Option A)

   • Not indicated for the presenting symptoms
   • No genital or urinary complaints mentioned in the history
   • Would not help diagnose the cause of neurological, cognitive, and abdominal symptoms 2

2. CT head (Option C)

   • While neurological symptoms are present, a CT head would be premature without first establishing the underlying cause
   • Radiation exposure is a concern in pediatric patients 2
   • Would be appropriate only after blood testing confirms lead poisoning and if there are concerns for encephalopathy

3. Psychiatry evaluation (Option D)

   • Inappropriate as the initial diagnostic approach for a child with physical symptoms and a clear temporal relationship to environmental change
   • Psychiatric evaluation may be helpful later for managing behavioral aspects of lead toxicity, but should not precede medical evaluation

Lead Poisoning: Key Considerations

Clinical Manifestations

• Neurological: Gait abnormalities, peripheral neuropathy, encephalopathy in severe cases
• Cognitive: Learning disabilities, decreased IQ, attention deficits
• Gastrointestinal: Abdominal pain, constipation, vomiting
• Hematological: Anemia, basophilic stippling on blood smear

Risk Factors

• Moving into an older home (pre-1978) with potential lead-based paint
• Renovation activities that disturb lead paint
• Contaminated soil, water, or imported products

Diagnostic Confirmation

After blood smear suggests lead poisoning:

1. Quantitative blood lead level testing
2. Complete blood count to assess severity of anemia
3. Additional tests based on severity (renal function, electrolytes)

Management Considerations

• Removal from the source of exposure
• Chelation therapy for elevated blood lead levels
• Nutritional support (iron, calcium, vitamin C)
• Neurodevelopmental follow-up
• Environmental assessment of the home

Conclusion

The clinical presentation strongly suggests lead poisoning, which is best initially evaluated with a blood smear to look for characteristic basophilic stippling. This approach is most appropriate given the constellation of neurological, cognitive, and gastrointestinal symptoms that developed after moving into a new house.