2‐[<scp>¹⁸F</scp>] <scp>FDG PET</scp>/<scp>CT</scp> in Rapid Late‐Onset Multiple Acyl‐<scp>CoA</scp> Dehydrogenase Deficiency: A Case Report

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare inborn metabolic myopathy affecting fat and protein metabolism. Patients with late-onset MADD typically present with exercise intolerance and muscle weakness. We present a patient with an acute, very late-onset symptom debut at 52 years of age. Over 5 months, the patient deteriorated from asymptomatic to almost complete loss of ambulation. He had a substantial weight loss, head-drop, progressive proximal limb and chewing weakness. Due to the rapid progression, amyotrophic lateral sclerosis, myositis, myasthenia gravis and a paraneoplastic syndrome in relation to underlying malignancy were considered first. A 2-[¹⁸F] FDG PET/CT scan was performed to exclude a paraneoplastic syndrome. The scan revealed diffuse and symmetric, pathologically high 2-[¹⁸F] FDG-uptake in the patient's neck, shoulder, and paravertebral muscles, which was later suggested as a sign of a metabolic myopathy. Muscle biopsy (Oil Red O staining) and acylcarnitine profile (elevated C5-C18 acylcarnitines) findings suggested MADD, which was confirmed by genetic analysis showing biallelic variants in the <i>ETFDH</i> gene (c.1763A>G, p.(His588Arg); c.897G>A, p.(Leu299=)). After 1 month of dietary intervention and daily diet supplements (riboflavin 400 mg TID, levocarnitine 1 g TID, Q10 150 mg qD in two doses), the patient had almost recovered to his habitual level. A posttreatment muscle biopsy showed less disrupted ultrastructure of the myofibers. We learned from this case of rapid and late-onset MADD that 2-[¹⁸F] FDG PET/CT, with diffuse and symmetric 2-[¹⁸F] FDG-uptake in skeletal muscle, can be valuable in clarifying this rare diagnosis.