Waddling Gait: A complication of valproate therapy and a thought beyond vitamin D deficiency

Area of Science:

• Paediatric Orthopaedics
• Neurology
• Clinical Pharmacology

Background:

• Proximal muscle weakness is common in paediatric orthopaedics, often attributed to vitamin D deficiency.
• Antiepileptic and antipsychotic drugs, like sodium valproate, are increasingly used in childhood disorders.
• Sodium valproate is known to cause a time-dependent, drug-induced proximal myopathy.

Observation:

• A 13-year-old female presented with an abnormal gait and was diagnosed with proximal myopathy.
• She was on combination therapy including sodium valproate for absence seizures and a mood disorder.
• Elevated serum alkaline phosphatase and creatine kinase myocardial band levels were noted.

Findings:

• The patient's proximal myopathy was confirmed through clinical investigations.
• Sodium valproate was identified as the likely cause of the drug-induced myopathy.
• Switching to ethosuximide and adding carnitine supplementation resolved the myopathy.

Implications:

• This case highlights the importance of considering drug-induced myopathy in children presenting with proximal weakness.
• It underscores the potential for misdiagnosis if medication side effects are not investigated.
• Accurate diagnosis and management of drug-induced proximal myopathy can lead to complete patient recovery.