Radiologic Findings in Gabapentin-Induced Myositis

Abstract

Throughout recent years, Gabapentin has become increasingly used for the treatment of neuropathic pain. We report on a case of a 31 year old female who presented to the emergency department with unilateral leg pain, weakness, and swelling after increasingly titrating her Gabapentin dosage over three weeks. Magnetic resonance imaging confirmed the presence of myositis confined to the left thigh and the patient's symptoms and laboratory abnormalities resolved following Gabapentin cessation. While Gabapentin-induced myositis and rhabdomyolysis is a rare entity, it should be a diagnostic consideration for radiologists, particularly in the absence of infection or trauma.

Keywords: CT; Case Report; Computed Tomography; Drug-Induced; Gabapentin; MRI; MSK; Magnetic Resonance Imaging; Musculoskeletal; Myopathy; Myositis; Rhabdomyolysis.

Figure 1

31 year old female with Gabapentin-induced myositis. Findings: Representative Doppler ultrasound image at the level of the left profundus femoris vein demonstrates normal laminar flow through the venous and arterial structures with diffuse areas of hypoechogenicity in the subcutaneous tissues of the left medial thigh. Technique: Doppler ultrasound of the left lower extremity with use of a 6.0 MHz linear probe.

Figure 2

31 year old female with Gabapentin-induced myositis. Findings: Axial (a) and coronal (b) images demonstrate increased circumference of the left leg with associated subcutaneous tissue edema and a large hypoattenuating lesion (arrows) involving the adductor compartment of the left medial thigh. Technique: Intravenous contrast enhanced arterial phase CT angiogram of the bilateral legs at the level of the mid-thigh.

Figure 3

31 year old female with Gabapentin-induced myositis. Findings: Coronal image demonstrates extensive subcutaneous edema (arrows) and increased inflammatory signal within the left adductor muscles (asterisk). Measurements comparing the relative diameters of the left and right thigh are also illustrated. Technique: Noncontrast coronal T2 Short Tau Inversion Recovery magnetic resonance imaging sequence.

Figure 4

31 year old female with Gabapentin-induced myositis. Findings: Coronal image demonstrates a large hyperintense lesion within the left adductor magnus (black asterisk), left gluteus medius (red asterisk), and left vastus lateralis (orange asterisk) muscles with extensive associated subcutaneous edema (arrows). Technique: Noncontrast coronal T2 Short Tau Inversion Recovery magnetic resonance imaging sequence.

Figure 5

31 year old female with Gabapentin-induced myositis. Findings: Axial fat suppressed image illustrates tracking of edema between the muscle compartments (arrows) and heterogeneous increased signal, predominantly within the left gluteus medius muscle (black asterisk), most compatible with inflammatory changes. Technique: Noncontrast axial T2 Short Tau Inversion Recovery magnetic resonance imaging sequence.

Figure 6

31 year old female with Gabapentin-induced myositis. Findings: Axial contrast enhanced image demonstrates areas of heterogeneous enhancement in the left adductor magnus muscle (arrows). Note is also made of inflammatory changes within the left adductor longus (black asterisk) and left gracilis (orange asterisk) muscles. Technique: Axial fat suppressed T1 magnetic resonance imaging sequence.

Figure 7

31 year old female with Gabapentin-induced myositis. Findings: Axial contrast enhanced image again demonstrates areas of inflammation and heterogeneous enhancement within the left gluteus medius (black asterisk) and left gluteus minimus (orange asterisk) muscles. Technique: Axial fat suppressed T1 magnetic resonance imaging sequence.

Figure 8

31 year old female with Gabapentin-induced myositis. Findings: Multiplanar noncontrast images demonstrate significant T2 hyperintensity involving the left gluteus medius (black asterisk - a ; red asterisk - b ; arrow - c), adductor magnus (black asterisk - b) and vastus lateralis (orange astrerisk - b) muscles along with fluid tracking between the muscle compartments (arrows - a) and extensive subcutaneous edema (arrows - b). Axial contrast enhanced images demonstrate heterogeneous enhancement of the left gluteus medius (black asterisk - d), gluteus minimus (orange asterisk - d) and adductor magnus muscles (arrows - e) as well as inflammatory changes involving the left adductor longus (black asterisk - e) and gracilis muscles (orange asterisk - e). Technique: Noncontrast axial (a), coronal (b) and sagittal (c) T2 Short Tau Inversion Recovery and axial contrast enhanced fat suppressed T1 (d,e) magnetic resonance imaging sequences.