Feasibility of 18F-FDG PET as a noninvasive diagnostic tool of muscle denervation: a preliminary study

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.

Higher Glycemic Index and Glycemic Load Diet Is Associated with Slower Disease Progression in Amyotrophic Lateral Sclerosis

OBJECTIVE

High-caloric diets may slow the progression of amyotrophic lateral sclerosis; however, key macronutrients have not been identified. We examined whether dietary macronutrients are associated with the rate of progression and length of survival among the prospective cohort study participants.

METHODS

Participants with a confirmed diagnosis of sporadic amyotrophic lateral sclerosis enrolled in the Multicenter Cohort Study of Oxidative Stress were included (n = 304). We evaluated baseline macronutrient intake assessed by food frequency questionnaire in relation to change in revised amyotrophic lateral sclerosis functional rating scale total-score, and tracheostomy-free survival using linear regression and Cox proportional hazard models. Baseline age, sex, disease duration, diagnostic certainty, body mass index, bulbar onset, revised amyotrophic lateral sclerosis functional rating scale total-score, and forced vital capacity were included as covariates.

RESULTS

Baseline higher glycemic index and load were associated with less decline of revised amyotrophic lateral sclerosis functional rating scale total score at 3-month follow-up (β = -0.13, 95% CI -0.2, -0.01, p = 0.03) and (β = -0.01, 95% CI -0.03, -0.0007, p = 0.04), respectively. Glycemic index second-quartile, third-quartile, and fourth-quartile groups were associated with less decline at 3 months by 1.9 (95% CI -3.3, -0.5, p = 0.008), 2.0 (95% CI -3.3, -0.6, p = 0.006), and 1.6 (95% CI -3.0, -0.2, p = 0.03) points compared with the first-quartile group; the glycemic load fourth-quartile group had 1.4 points less decline compared with the first-quartile group (95% CI -2.8, 0.1, p = 0.07). Higher glycemic index was associated with a trend toward longer tracheostomy-free survival (HR 0.97, 95% CI 0.93, 1.00, p = 0.07).

INTERPRETATION

Higher dietary glycemic index and load are associated with slower disease progression in amyotrophic lateral sclerosis. ANN NEUROL 2024;95:217-229.

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.

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.

Diagnostic Efficacy of 18F-FDG PET/MRI in Peripheral Nerve Injury Models

The aim of this study was to evaluate the diagnostic efficacy of ¹⁸F-FDG PET/MRI in two different peripheral neuropathic pain models using the injured rat sciatic nerves. Twelve rats, with operation on left sciatic nerves, were evenly divided into three groups: sham surgery (control group), crushing injury and chronic constriction injury (CCI) (experimental groups). The nerve damage was assessed at 3 weeks postoperatively using following methods: paw withdrawal threshold values (RevWT), maximum standardized uptake values on PET/MRI images (SUVR), and counting the number of myelinated axons in proximal and distal sites of nerve injury (MAxR). The results were quantified and statistically analyzed. Compared to the control group, the crushing injury demonstrated significant differences in RevWT (p < 0.0001) and SUVR (p = 0.027) and the CCI group demonstrated significant differences in RevWT (p < 0.0001), SUVR (p = 0.001) and MAxR (p = 0.048). There were no significant differences between the two experimental groups for all assessments. Correlation analysis demonstrated that RevWT and SUVR assessments were highly correlated (r = -- 0.710, p = 0.010), and SUVR and MAxR were highly correlated (r = 0.611, p = 0.035). However, there was no significant correlation between RevWT and MAxR. The PET scan may be a valuable imaging modality to enable noninvasive, objective diagnosis of neuropathic pain caused by peripheral nerve injury. Also, MRI fused with PET may help clarify the anatomic location of soft tissue structures, including the peripheral nerves.

Noninvasive evaluation of fat-carbohydrate metabolic switching in heart and contracting skeletal muscle

The ability of heart and skeletal muscle (SM) to switch between fat and carbohydrate oxidation is of high interest in the study of metabolic diseases and exercise physiology. Positron emission tomography (PET) imaging with the glucose analog 2-[¹⁸F]fluoro-2-deoxy-glucose (¹⁸F-FDG) provides a noninvasive means to quantitate glucose metabolic rates. However, evaluation of fatty acid oxidation (FAO) rates by PET has been limited by the lack of a suitable FAO probe. We have developed a metabolically trapped oleate analog, ( Z)-18-[¹⁸F]fluoro-4-thia-octadec-9-enoate (¹⁸F-FTO), and investigated the feasibility of using ¹⁸F-FTO and ¹⁸F-FDG to measure FAO and glucose uptake, respectively, in heart and SM of rats in vivo. To enhance the metabolic rates in SM, the vastus lateralis (VL) muscle was electrically stimulated in fasted rats for 30 min before and 30 min following radiotracer injection. The responses of radiotracer uptake patterns to pharmacological inhibition of FAO were assessed by pretreatment of the rats with the carnitine palmitoyl-transferase-1 (CPT-1) inhibitor sodium 2-[5-(4-chlorophenyl)-pentyl]oxirane-2-carboxylate (POCA). Small-animal PET images and biodistribution data with ¹⁸F-FTO and ¹⁸F-FDG demonstrated profound metabolic switching for energy provision in the myocardium from exogenous fatty acids to glucose in control and CPT-1-inhibited rats, respectively. Uptake of both radiotracers was low in unstimulated SM. In stimulated VL muscle, ¹⁸F-FTO and ¹⁸F-FDG uptakes were increased 4.4- and 28-fold, respectively, and CPT-1 inhibition only affected ¹⁸F-FTO uptake (66% decrease). ¹⁸F-FTO is a FAO-dependent PET probe that may allow assessment of energy substrate metabolic switching in conjunction with ¹⁸F-FDG and other metabolic probes.

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

BACKGROUND

Glucose hypermetabolism in denervated skeletal muscle suggests the potential for developing a diagnostic tool for peripheral nerve injuries. Herein, we investigated the characteristics and molecular mechanism of this phenomenon.

NEW METHOD

Temporal course of glucose hypermetabolism and development of abnormal spontaneous activities (ASA) through electromyography (EMG) were investigated in rats with complete sciatic nerve injuries. Rats with partial sciatic nerve injuries were used to investigate the relationship between nerve injury severity and change in glucose metabolism. Rapamycin-treated rats were used to study molecular mechanism. Mean lesion-to-normal count ratios (LNR_mean) was calculated as a numeric value of the ¹⁸F-FDG uptake.

RESULTS

Glucose hypermetabolism began 2 days after nerve injury and lasted up to 12 weeks, with the maximum increase at 1 week after denervation (10-fold increase compared to sham-operated muscle; LNR_mean, sham, 1.360 ± 0.452; denervation, 10.340 ± 4.094; n = 5; P < 0.05). The metabolic changes showed similar temporal characteristics to ASA on EMG. The signal intensity of ¹⁸F-FDG uptake in denervated skeletal muscle was strongly related to nerve injury severity in a partial nerve injury model (Pearson correlation coefficient 0.63, P < 0.05). Suppression of mTOR by rapamycin treatment reduced the increase in peak glucose hypermetabolism in muscle denervation.

COMPARISON WITH EXISTING METHOD

Metabolic changes in ¹⁸F-FDG PET scans have a wider time span than abnormalities on EMG after denervation and it is correlated with the severity of nerve injury assessed by NCS.

CONCLUSIONS

¹⁸F-FDG PET may be used to diagnose and evaluate peripheral nerve injuries.

Transplantation of human mobilized mononuclear cells improved diabetic neuropathy

Rodent stem cells demonstrated regenerative effects in diabetic neuropathy via improvement in nerve perfusion. As a pre-clinical step, we explored if human mobilized mononuclear cells (hMNC) would have the same effects in rats. hMNC were injected into Rt. hind-limb muscles of streptozotocin-induced diabetic nude rats, and the grafts were monitored using with MRI. After 4 weeks, the effects were compared with those in the vehicle-injected Lt. hind limbs. Nerve conduction, muscle perfusion and gene expression of sciatic nerves were assessed. Induction of diabetes decreased nerve function and expression of Mpz and Met in the sciatic nerves, which are related with myelination. hMNC injection significantly improved the amplitude of compound muscle action potentials along with muscle perfusion and sciatic nerve Mpz expression. On MRI, hypointense signals were observed for 4 weeks at the graft site, but their correlation with the presence of hMNC was detectable for only 1 week. To evaluate paracrine effects of hMNC, IMS32 cells were tested with hepatocyte growth factor (HGF), which had been reported as a myelination-related factor from stem cells. We could observe that HGF enhanced Mpz expression in the IMS32 cells. Because hMNC secreted HGF, IMS32 cells were co-cultured with hMNC, and the expression of Mpz increased along with morphologic maturation. The hMNC-induced Mpz expression was abrogated by treatment of anti-HGF. These results suggest that hMNC could improve diabetic neuropathy, possibly through enhancement of myelination as well as perfusion. According to in vitro studies, HGF was involved in the hMNC-induced myelination activity, at least in part.

Atypical 18F-FDG PET-CT uptake in the head and neck; a case-based pictorial review

Positron emission tomography - computed tomography (PET-CT) with fluorine-18-fluorodeoxy-d-glucose (¹⁸F-FDG) has an increasing role in head and neck imaging. Interpretation of ¹⁸F-FDG-tracer uptake in the head and neck requires an understanding of normal physiological patterns of tracer uptake, as well as knowledge of potential pitfalls and atypical patterns. This article presents a select series of unusual patterns of ¹⁸F-FDG uptake on PET-CT imaging of the head and neck.

Longitudinal Changes in Glucose Metabolism of Denervated Muscle after Complete Peripheral Nerve Injury

PURPOSE

Electrodiagnostic studies can obtain information 2 or 3 weeks after an acute nerve injury. Previous studies have shown increased glucose metabolism in denervated muscles 1 week after injury using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) positron emission tomography (PET). Therefore, this study aimed to evaluate the changes in glucose metabolism in denervated muscles using serial monitoring by [(18)F]FDG PET scans.

PROCEDURES

Denervation was induced in eight male Sprague-Dawley rats (aged 7 weeks old) weighing 200-250 g. The right legs of the rats were denervated by resecting the sciatic nerve in the thigh after the initial skin incision. Two rats were sacrificed 1 and 10 weeks after denervation. Skeletal muscles (gastrocnemius and tibialis anterior) were excised from both the right and left legs of the rats. Staining with hematoxylin and eosin, glucose transporter (GLUT)-1, GLUT-4, and hexokinase II was undertaken. PET/computed tomography (CT) scans were performed on the six remaining rats a total of five times at 1, 2, 5, 8, and 10 weeks after denervation. Regions of interest were drawn on integrated PET/CT images to measure the degree of [(18)F]FDG uptake in the right and left lower leg muscles. Target-to-background ratios (TBRs) were calculated by dividing the FDG uptake of the lower leg muscles by that of the upper leg muscles.

RESULTS

The TBRs of the denervated muscles were higher than those of the control muscles at both 1 (6.84 ± 1.98 vs. 1.18 ± 0.11, p = 0.009) and 2 (4.10 ± 2.05 vs. 1.86 ± 0.73, p = 0.0374) weeks after denervation. After 5 (2.18 ± 0.78 vs. 1.35 ± 0.47, p = 0.1489), 8 (1.76 ± 0.18 vs. 1.69 ± 0.18, p = 0.5127), and 10 (1.76 ± 0.52 vs. 1.56 ± 0.37, p = 0.5637) weeks, the difference in the TBRs between the denervated and controls became non-significant.

CONCLUSIONS

[(18)F]FDG PET can visualize increased glucose metabolism in a denervated muscle early as 1 week after injury. Therefore, PET could be adopted as a noninvasive imaging modality for acute nerve injuries. In addition, [(18)F]FDG PET may help to understand the role of the nervous system in the control of peripheral tissues.

Denervation in Femoral Artery-Ligated Hindlimbs Diminishes Ischemic Recovery Primarily via Impaired Arteriogenesis

Aims

Multiple factors regulate arteriogenesis. Peripheral nerves play a crucial role in vascular remodeling, but the function of peripheral nerves during arteriogenesis is obscure. Our study investigated the contribution of denervation to arteriogenesis during post-ischemic recovery from hindlimb femoral artery ligation.

Methods and Results

Sprague-Dawley rats were randomly allocated into four groups of normal control (NC), hindlimb ischemia (HI), hindlimb ischemia with denervation (HID) and hindlimb simple denervation (HD). Hindlimb ischemic recovery was assessed by clinical assessment and tibialis anterior muscle remodeling on day 28 post-surgery. Blood flow was determined by laser Doppler imaging on day 0, 3, 7, 14 and 28 post-surgery. Collateral number of hindlimb was observed by angiography and gracilis muscles were tested by immunostaining on day 7 and 28 post-surgery. Angiogenesis was accessed by counting CD31 positive capillaries in tibialis anterior muscles on day 28 post-surgery. Group HID showed impaired ischemic recovery compared with the other 3 groups and impaired blood flow recovery compared with group HI on day 28 post-surgery. The collateral number and capillary density of group HID were lower than group HI. The collateral diameter of both group HID and group HI significantly increased compared with group NC. However, the lumen diameter was much narrower and the vessel wall was much thicker in group HID than group HI. We also demonstrated that the thickened neointima of collaterals in group HID comprised of smooth muscle cells and endothelial cells.

Conclusions

Denervation of the ligated femoral artery in the hindlimb impairs ischemic recovery via impaired perfusion. The possible mechanisms of impaired perfusion are lower collateral number, lower capillary density and most likely narrower lumen, which damage ischemic recovery. This study illustrates the crucial role of peripheral nerves in arteriogenesis using a model combined ischemia with denervation in hindlimb.

Increased (18)F-FDG uptake in the trapezius muscle in patients with spinal accessory neuropathy

To investigate (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) signal changes of denervated muscles in patients with electrophysiologically confirmed neuropathy.

METHODS

This is a case series of three cancer patients who were referred to the electromyography laboratory in 2013 due to shoulder discomfort after surgery including neck dissection. Spinal accessory neuropathy was diagnosed based on electrophysiological studies. Patients' medical history, electrophysiological data, and FDG-PET images were reviewed retrospectively. Mean standard uptake values (SUV) of trapezius muscles were measured.

RESULTS

The patients (3 men, aged 61-78years) showed spinal accessory neuropathy with different degrees of severity. In all patients, preoperative or postoperative FDG-PET showed increased FDG uptake in the ipsilateral trapezius muscle. These results were compatible with previously reported glucose hypermetabolism in denervated skeletal muscles.

CONCLUSION

This is the first clinical report of increased FDG uptake by denervated muscles in electrophysiologically confirmed neuropathy.

Evaluation of Avulsion-Induced Neuropathology in Rat Spinal Cords with 18F-FDG Micro-PET/CT

Brachial plexus root avulsion (BPRA) leads to dramatic motoneuron death and glial reactions in the corresponding spinal segments at the late stage of injury. To protect spinal motoneurons, assessment of the affected spinal segments should be done at an earlier stage of the injury. In this study, we employed ¹⁸F-FDG small-animal PET/CT to assess the severity of BPRA-induced cervical spinal cord injuries. Adult Sprague-Dawley rats were randomly treated and divided into three groups: Av+NS (brachial plexus root avulsion (Av) treated with normal saline), Av+GM1 (treated with monosialoganglioside), and control. At time points of 3 day (d), 1 week (w), 2 w, 4 w and 8 w post-injury, ¹⁸F-FDG micro-PET/CT scans and neuropathology assessments of the injured spinal roots, as well as the spinal cord, were performed. The outcomes of the different treatments were compared. The results showed that BPRA induced local bleeding and typical Wallerian degeneration of the avulsed roots accompanied by ¹⁸F-FDG accumulations at the ipsilateral cervical intervertebral foramen. BPRA-induced astrocyte reactions and overexpression of neuronal nitric oxide synthase in the motoneurons correlated with higher ¹⁸F-FDG uptake in the ipsilateral cervical spinal cord during the first 2 w post-injury. The GM1 treatment reduced BPRA-induced astrocyte reactions and inhibited the de novo nNOS expressions in spinal motoneurons. The GM1 treatment also protected spinal motoneurons from avulsion within the first 4 w post-injury. The data from this study suggest that ¹⁸F-FDG PET/CT could be used to assess the severity of BPRA-induced primary and secondary injuries in the spinal cord. Furthermore, GM1 is an effective drug for reducing primary and secondary spinal cord injuries following BPRA.