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An Intriguing Case of Acute Left-Sided Weakness in a 4-Year-Old Boy

A 4-year-old male presented with a 1-day history of sudden-onset left-sided upper and lower extremity weakness with difficulty walking. No history of constitutional symptoms, trauma, recent illness, or fever was present. The patient had a previous hospitalization at 21 months of age with acute generalized weakness and behavioral changes following a diarrheal and upper respiratory illness. At that time, metabolic workup was significant for elevated capillary gas lactate (2.5 mmol/L, upper limit of normal [ULN] 1.27), and a minimally elevated NH3 (40 μmol/L, ULN 34 μmol/L); serum lactate was not obtained. Magnetic resonance imaging (MRI) showed asymmetric bilateral abnormalities in the brainstem and cervical spine and the patient was diagnosed with acute disseminated encephalomyelitis (ADEM), treated with intravenous immunoglobulin, and he experienced a complete recovery. No family history of mitochondrial or metabolic disorders, neuromuscular disease, or early childhood mortality. Parents denied consanguinity. Social and surgical histories were unremarkable. Physical examination showed a normocephalic, alert and oriented child with appropriate affect. Cranial nerves, sensory examination, and deep tendon reflexes were normal. Strength was 4/5 in the left upper and left lower extremities with left foot dragging on ambulation. MRI of the brain and cervical spine without contrast with spectroscopy demonstrated bilateral and asymmetrical increased T2 and decreased T1 signal in the globus pallidi (GP; Figures 1 and 2), cerebral peduncles, substantia nigra, and mildly increased T2 signal in the posterior cervical and proximal thoracic spinal cord. Magnetic resonance spectroscopy (MRS) analysis demonstrated a lactate peak in the right GP (Figure 3). Laboratory studies included normal complete blood count and basic chemistries. Plasma amino acid analysis revealed marked hyperalaninemia at 1.579 μmol/L (ULN 450 μmol/L), and hyperprolinemia at 684 μmol/L (ULN 290 μmol/L), suggesting a state of lactic acidosis. However, serum lactic acid was only modestly elevated at 2.5 mmol/L (reference range 0.4-2.0 mmol/L). Cerebrospinal fluid analysis showed elevated lactic acid (3.4 mmol/L, ULN 2.8 mmol/L), negative oligoclonal bands, and negative cultures. Due to the similarity of this presentation to the child’s previous event at age 21 months, he was started on high-dose corticosteroids for suspected atypical ADEM. Subsequently, the patient became acutely agitated, developed spasticity of the right side and increased weakness of the left, with slurred speech, drooling, and trismus. Due to this unexpected adverse event, a possible neurometabolic etiology was suspected and steroids were withdrawn; the patient was transferred to pediatric intensive care unit and given baclofen for muscle spasms.