18F-FDG positron emission tomography as a novel diagnostic tool for peripheral nerve injury

FDG uptake in the cervical muscles after neck dissection: imaging features and postoperative natural course on 18F‑FDG‑PET/CT

PURPOSE

This study aimed to assess the imaging features and postoperative natural course of 18F-fluorodeoxyglucose (FDG) uptake in the cervical muscles after neck dissection.

MATERIALS AND METHODS

This study included 83 patients who underwent preoperative and postoperative 18F-FDG-PET/CT and were diagnosed with head and neck malignancy after neck dissection. Postoperative 18F-FDG-PET/CT was performed within 5 years after neck dissection. Preoperative and postoperative FDG uptake of the trapezius, sternocleidomastoid, scalene, pectoralis major, and deltoid muscles was visually assessed. Increased postoperative uptake was visually defined as higher postoperative FDG uptake than the preoperative one in the corresponding muscle. The maximum standardized uptake value (SUVmax) was measured in cases with increased postoperative uptakes.

RESULTS

Increased postoperative uptakes were observed in 43 patients (52%). The trapezius (31/83, 37%), sternocleidomastoid (19/83, 23%), and scalene (12/83, 14%) muscles were involved, as opposed to the pectoralis major and deltoid muscles were not. Increased postoperative uptakes were observed on the dissected side in all 43 patients. Significant differences between SUVmax estimated from the mixed-effects model and postoperative months were observed in the trapezius muscle (Coefficient (β) = -0.038; 95% confidence interval (CI): [-0.047, -0.028]; p < 0.001) and sternocleidomastoid muscle (β =  -0.015; 95% CI: [-0.029, -0.001]; p = 0.046).

CONCLUSIONS

Increased postoperative uptakes in the cervical muscles were observed on the dissected side in approximately half of the patients after neck dissection. The SUVmax in the trapezius and sternocleidomastoid muscles decreased after surgery over time.

18F-ASEM PET/MRI targeting alpha7-nicotinic acetylcholine receptor can reveal skeletal muscle denervation

BACKGROUND

The increased expression of the nicotinic acetylcholine receptor (nAChR) in muscle denervation is thought to be associated with electrophysiological acetylcholine supersensitivity after nerve injury. Hence, we investigated the utility of the 18F-ASEM alpha7-nAChR targeting radiotracer as a new diagnostic method by visualizing skeletal muscle denervation in mouse models of sciatic nerve injury.

METHODS

Ten-week-old C57BL/6 male mice were utilized. The mice were anesthetized, and the left sciatic nerve was resected after splitting the gluteal muscle. One week (n = 11) and three weeks (n = 6) after the denervation, 18F-ASEM positron emission tomography/magnetic resonance imaging (PET/MRI) was acquired. Maximum standardized uptake values (SUVmax) of the tibialis anterior muscle were measured for the denervated side and the control side. Autoradiographic evaluation was performed to measure the mean counts of the denervated and control tibialis anterior muscles at one week. In addition, immunohistochemistry was used to identify alpha7-nAChR-positive areas in denervated and control tibialis anterior muscles at one week (n = 6). Furthermore, a blocking study was conducted with methyllycaconitine (MLA, n = 5).

RESULTS

18F-ASEM PET/MRI showed significantly increased 18F-ASEM uptake in the denervated tibialis anterior muscle relative to the control side one week and three weeks post-denervation. SUVmax of the denervated muscles at one week and three weeks showed significantly higher uptake than the control (P = 0.0033 and 0.0277, respectively). The relative uptake by autoradiography for the denervated muscle was significantly higher than in the control, and immunohistochemistry revealed significantly greater alpha7-nAChR expression in the denervated muscle (P = 0.0277). In addition, the blocking study showed no significant 18F-ASEM uptake in the denervated side when compared to the control (P = 0.0796).

CONCLUSIONS

Our results suggest that nAChR imaging with 18F-ASEM has potential as a noninvasive diagnostic method for peripheral nervous system disorders.

Increased 18 F-FDG uptake in denervated muscles in a case of Parsonage-Turner syndrome

BACKGROUND

Parsonage-Turner Syndrome (PTS) is a rare brachial plexopathy characterized by the sudden onset of pain in the shoulder girdle followed by upper limb weakness. PTS is frequently under-recognized or misdiagnosed as other more common neurological disorders presenting in a similar fashion, such as cervical radiculopathy which may require surgical intervention. Accurate diagnosis and prompt management implicate a good prognosis. Although electrophysiological studies are considered the most important for evaluating peripheral nerve injuries, it usually takes time, up to 3 weeks after the initial insult of the nerve for electromyogram (EMG) and nerve conduction studies (NCS) to display abnormalities. In the cases of PTS, especially when initial EMG/NCS and magnetic resonance neurography (MRN) results are inconclusive, ¹⁸ F-FDG positron emission tomography and computed tomography (¹⁸ F-FDG PET-CT) may be useful in helping the early detection of muscle denervation.

CASE PRESENTATION

A 60-year-old right-handed Taiwanese woman presented with sudden onset of intense and sharp left shoulder girdle pain without radiating to the arm, followed by muscle weakness of her left arm in abduction and elevation 3 days after the onset of pain. A detailed neurological examination and EMG and NCS suggested the clinical diagnosis of left brachial plexopathy. MRN imaging revealed no significant abnormality. ¹⁸ F-FDG PET-CT showed increased uptake in denervated muscles (supraspinatus, deltoid, and biceps muscles). Treatment with oral prednisolone and physiotherapy significantly improved pain and muscle weakness.

CONCLUSIONS

We present increased ¹⁸ F-FDG uptake in denervated muscles detected by ¹⁸ F-FDG PET-CT. ¹⁸ F-FDG PET-CT may serve as an adjunct examination to evaluate PTS, which has been suggested previously but rarely reported.

Repetitive transcranial magnetic stimulation regulates neuroinflammation, relieves hyperalgesia and reverses despair-like behaviour in chronic constriction injury rats

Repetitive transcranial magnetic stimulation (rTMS) could effectively relieve the pain and depression in neuropathic pain (NP) patients. However, the specific treatment parameters and exact mechanism are still unclear. Our purpose is to observe the effects of rTMS on pain and despair-like behaviour in chronic constriction injury (CCI) rats and explore its possible mechanism. Thirty-two 8-week-old male Sprague-Dawley rats were randomly divided into four groups: sham operation group (S, n = 8), CCI group (n = 8), 1 Hz-rTMS group (n = 8) and 10 Hz-rTMS group (n = 8). The rTMS was applied to the left dorsal anterior agranular insular (AId) 1 week after the operation, once a day, 5 days/week for 4 consecutive weeks. Mechanical hyperalgesia, despair-like behaviours and sciatic nerve function were used to evaluate the effects of rTMS. Besides, glucose metabolism, the metabotropic glutamate receptors 5 (mGluR5), N-Methyl-D-Aspartic acid receptor type 2B (NMDAR2B), tumour necrosis factor-α (TNF-α), interleukin-6 (Ll-6) and interleukin-1β (Ll-1β) in AId were tested to explore the possible mechanism. Compared with 1 Hz-rTMS, the rats of 10 Hz-rTMS had higher the mechanical hyperalgesia, higher sugar preference and shorter swimming immobility time. Besides, the expressions of mGluR5, NMDAR2B, TNF-α, Ll-1β and Ll-6 both in 1 Hz-rTMS and 10 Hz-rTMS groups were reduced compared with the CCI group; the 10 Hz-rTMS group had a more decrease than that of 1 Hz-rTMS. Furthermore, the [18]F-FDG uptake was lower than that in the 1 Hz-rTMS group. Compared with 1 Hz-rTMS, 10 Hz-rTMS could more effectively relieve mechanical hyperalgesia and reverse despair-like behaviour in rats. The mechanism could be related to regulating mGluR5/NMDAR2B-related inflammatory signalling pathways in the AId.

18 F-FDG uptake in denervated muscles of patients with peripheral nerve injury

OBJECTIVE

We aimed to investigate the clinical significance of increased uptake in ¹⁸ F-fluorodeoxyglucose positron emission tomography in patients with peripheral nerve lesions.

METHODS

We selected patients with unilateral peripheral nerve lesions confirmed with electromyography who had undergone ¹⁸ F-fluorodeoxyglucose positron emission tomography covering the lesions. In the denervated muscles and their contralateral corresponding pairs, a mean (SUVmean) and maximum standardized uptake value (SUVmax) were obtained from ¹⁸ F-fluorodeoxyglucose positron emission tomography images. We analyzed the difference in these values between the denervated and normal muscles. The lesion-to-normal ratio of the SUVmean (LNRmean) between each muscle pair was also obtained. Subgroup analysis was performed to find whether these three parameters were related to severity, abundance of abnormal spontaneous activity, and etiology.

RESULTS

Twenty-three patients with 38 denervated muscles were included. Compared to their normal counterparts, the denervated muscles showed significantly higher SUVmax (1.33 ± 0.49 vs. 1.10 ± 0.37, n = 38, P < 0.001) and SUVmean (0.91 ± 0.31 vs. 0.77 ± 0.28, n = 38, P < 0.001). The muscles with severe neuropathy showed significantly higher LNRmean than those with mild neuropathy (1.30 ± 0.36, n = 19 vs. 1.11 ± 0.24, n = 19; P = 0.046), and the muscles with traumatic neuropathy showed significantly higher LNRmean than those with nontraumatic neuropathy (1.32 ± 0.28, n = 13 vs. 1.14 ± 0.33, n = 23; P = 0.015).

INTERPRETATION

Denervated muscles with peripheral nerve injury showed higher uptake than normal muscles in ¹⁸ F-fluorodeoxyglucose positron emission tomography, and this was associated with severity and etiology.

Imaging in the repair of peripheral nerve injury

Surgical intervention followed by physical therapy remains the major way to repair damaged nerves and restore function. Imaging constitutes promising, yet underutilized, approaches to improve surgical and postoperative techniques. Dedicated methods for imaging nerve regeneration will potentially provide surgical guidance, enable recovery monitoring and postrepair intervention, elucidate failure mechanisms and optimize preclinical procedures. Herein, we present an outline of promising innovations in imaging-based tracking of in vivo peripheral nerve regeneration. We emphasize optical imaging because of its cost, versatility, relatively low toxicity and sensitivity. We discuss the use of targeted probes and contrast agents (small molecules and nanoparticles) to facilitate nerve regeneration imaging and the engineering of grafts that could be used to track nerve repair. We also discuss how new imaging methods might overcome the most significant challenges in nerve injury treatment.