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

## TL;DR

A rare metabolic muscle disease was diagnosed using a PET/CT scan, which showed unusual patterns in muscle uptake, leading to a successful treatment plan.

## Contribution

Demonstrates the utility of 2‐[18F] FDG PET/CT in diagnosing late-onset multiple acyl-CoA dehydrogenase deficiency.

## Key findings

- 2‐[18F] FDG PET/CT revealed diffuse and symmetric muscle uptake, indicating a metabolic myopathy.
- Genetic analysis confirmed biallelic ETFDH gene variants causing MADD.
- Dietary intervention and supplements led to significant clinical improvement.

## Abstract

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 ETFDH 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.