Coexistence of VLCAD deficiency and Hashimoto's thyroiditis: a rare case report

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a mitochondrial fatty acid oxidation disorder caused by mutations in the acyl-CoA dehydrogenase very long chain (ACADVL) gene. Hashimoto's thyroiditis is the most common autoimmune thyroid disease. To the best of our knowledge, their coexistence has not been reported. This case highlights a potential mechanistic link between mitochondrial dysfunction, chronic inflammation, and endocrine autoimmunity.

A 33-year-old woman presented with acute-onset generalized myalgia, fatigue, and dark-colored urine. Laboratory findings confirmed severe rhabdomyolysis. Thyroid tests revealed primary hypothyroidism with elevated anti-TPO and anti-Tg levels, and ultrasonography demonstrated chronic autoimmune thyroiditis. The patient had a history of recurrent unexplained rhabdomyolysis without identifiable external triggers. Therefore, genetic testing was performed to evaluate for an underlying metabolic myopathy. Genetic testing identified a homozygous ACADVL c.1097G>A (p. Arg366His) variant, confirming VLCAD deficiency. Treatment included intravenous hydration, L-carnitine supplementation, a medium-chain triglyceride (MCT)-enriched diet, and levothyroxine. The patient showed marked improvement and remained stable without recurrence for one year.

To the best of our knowledge, this appears to be the first report describing the coexistence of VLCAD deficiency and Hashimoto's thyroiditis. Chronic mitochondrial dysfunction may potentially contribute to systemic inflammation and immune activation associated with autoimmune thyroid disease. Increased awareness of this association may facilitate earlier clinical recognition and encourage comprehensive evaluation.