*Corresponding author: Youngwon Lee College of Veterinary Medicine, Research Institute of Veterinary Medicine, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Korea Hypertrophic ganglioneuritis is a rare inflammatory condition in humans and animals that is, characterized by enlargement of the spinal cord nerve roots [1-4]. The etiology of hypertrophic ganglioneuritis is poorly understood. In human medicine, hypertrophic cervical neuritis is often described as chronic inflammatory demyelinating polyneuropathy (CIDP), with a prevalence of 7.00 per 100,000 individuals [3]. The main clinical findings are insidious onset, gait ataxia, and sensory symptoms [4].
Some studies have reported canine hypertrophic ganglioneuritis predominantly occurring in large breeds [1,2]. Hypertrophic ganglioneuritis in cats is rare, with only two cases involving the brachial plexuses [5,6]. The limited reports available described the magnetic resonance imaging (MRI) findings of hypertrophic ganglioneuritis in dogs. In all 13 canine cases, the lesion was localized to the C2 spinal nerve roots. Only a single case of a Yorkshire Terrier exhibiting unilateral C2 nerve root enlargement has been reported. All other reported cases showed bilateral hypertrophy of the C2 nerve roots. This bilateral symmetry helps distinguish hypertrophic ganglioneuritis from other conditions, such as neoplastic lesions, which are typically unilateral. The hypertrophied nerve roots can cause varying degrees of spinal cord compression and distortion [1,2]. This report presents the imaging features of suspected hypertrophic ganglioneuritis in a small-breed dog, along with the follow-up MRI findings after non-surgical medical treatment.
A six-year-old, 5.8 kg intact male Yorkshire Terrier presented with a five-month history of progressive ataxia affecting the thoracic and pelvic limbs. The owner reported no history of trauma. The dog had been treated with non-steroidal anti-inflammatory drugs for two months at a local veterinary clinic without clinical improvement
The physical examination revealed a pain response upon ventral flexion of the neck. Gait analysis revealed proprioceptive ataxia. A neurological examination indicated upper motor neuron signs in the thoracic and pelvic limbs, while the cranial nerve function remained normal. The postural reactions were absent in the right thoracic limb and delayed in the left thoracic limb and both pelvic limbs. These findings suggested a lesion in the C1-5 spinal cord segments. The differential diagnoses included intervertebral disc disease (IVDD), neoplastic processes, and inflammatory conditions.
Cervical spine radiographs showed mild narrowing of the disc spaces at C2-3, C4-5, and C5-6, suggesting possible IVDD and spondylosis deformans at C2-3. A further evaluation with a cervical spine MRI (1.5 Tesla unit, Vantage Elan; Canon Medical Systems, Japan) revealed bilateral hypertrophy of the C2 nerve roots on the dorsal and transverse plane, measuring approximately 4 mm and 3.1 mm for the left and the right on the transverse plane, respectively. The hypertrophied nerve roots showed hyperintensity on the T2-weighted and T2-weighted fluid-attenuated inversion recovery (FLAIR) images and hypointensity on the T1-weighted images with prominent contrast enhancement on the post-contrast T1-weighted images (Fig. 1). The enlarged nerve roots were located at the intradural extramedullary level, appearing as less than half the size of the dorsal nerve rootlets on the transverse plane. These enlarged nerve roots caused moderate spinal cord compression, resulting in a triangular distortion of the spinal cord on the transverse plane (Fig. 2). The adjacent spinal cord parenchyma exhibited high signal intensity on the T2 weighted and FLAIR images, and isointensity on the T1-weighted images without contrast enhancement.
On the sagittal plane, a high T2 signal, low T1 signal, and low FLAIR signal area were observed on the dorsal side of the C2 level spinal cord. These findings are consistent with syringomyelia, presenting as a rod-shaped signal abnormality along the dorsal aspect of the central canal in the transverse plane. In addition, mild intervertebral disc protrusions were observed at C4-5, C5-6, and C6-7, compressing the spinal cord parenchyma by less than 10%. Overall degenerative dehydration of the cervical intervertebral disc materials was observed with low T2 signal intensity.
The brain MRI revealed mild dilation of the third and fourth ventricles, with no other significant findings in the brain parenchyma. Analysis of the cerebrospinal fluid (CSF) revealed clear, colorless fluid with a total nuclear cell count of 2 cells/μL, within the reference interval. Cytology revealed 59% mononuclear cells, 18% neutrophils, and 22% lymphocytes. The polymerase chain reaction test for infectious agents was negative.
Considering the hypertrophy of the C2 nerve roots, the differential diagnosis included neoplastic conditions such as peripheral nerve sheath tumors (PNST) or lymphoma, and inflammatory conditions such as hypertrophic ganglioneuritis. Although the patient exhibited mild cervical IVDD, less than 10% compression of the spinal cord parenchyma was deemed insufficient to account for the clinical symptoms. Considering the bilateral and symmetric hypertrophy of the C2 nerve roots, hypertrophic ganglioneuritis was prioritized as the most likely diagnosis. Therefore, an immunosuppressive dose of steroids was initiated as a diagnostic treatment.
The patient was prescribed prednisolone (1 mg/kg per oral q12 hours [PO q12h]), pregabalin (2 mg/kg PO q12h), and methocarbamol (15 mg/kg PO q12h) starting from the day of the MRI. The dog showed consistent improvement in gait from the second day of medication. The treatment continued for approximately three months until the follow-up MRI.
The follow-up MRI revealed a decrease in the previously observed hypertrophy of the bilateral C2 nerve roots. The left C2 nerve root measured approximately 2.9 mm, and the right C2 nerve root measured approximately 2.7 mm, both showing a significant reduction compared to the first examination, which was performed three months earlier. The nerve roots continued to exhibit prominent contrast enhancement on the T1-weighted images after contrast administration, consistent with previous findings. The previously noted spinal cord compression caused by the hypertrophied bilateral nerve roots in the transverse plane was alleviated. Post-treatment MRI showed that the spinal cord exhibited only mild compression with slight lateral shape changes (Fig. 3). The medical treatment was maintained, and the dog continued to exhibit normal gait.
Hypertrophic ganglioneuritis is a rare inflammatory condition that has been documented in both humans and animals, with an unknown origin. In human medicine, hypertrophic cervical neuritis is frequently referred to as CIDP, which is the most common chronic immune-mediated inflammatory polyneuropathy and includes various subtypes. CIDP is classified into two forms: typical and atypical. Typical CIDP is a symmetrical polyneuropathy affecting both proximal and distal muscles, whereas atypical forms include ‘distal acquired demyelinating symmetric and multifocal acquired demyelinating sensory and motor neuropathy, or Lewis-Sumner syndrome' [7]. In human medicine, onion bulb formation, caused by Schwann cell proliferation following cycles of demyelination and remyelination, is characteristic of CIDP. In dogs and cats, however, hypertrophic neuritis is usually accompanied by chronic lymphocytic inflammation rather than onion bulb formation. Thus, hypertrophic neuritis might represent different pathological entities in humans and animals [1,2,5].
Hypertrophic ganglioneuritis is diagnosed primarily through histopathology and MRI and is characterized by significant nerve root hypertrophy [8,9]. The causes of spinal nerve enlargement in dogs encompass neoplastic conditions such as PNST or lymphomas, inflammatory neuritis (both infectious and non-infectious), and trauma. Nevertheless, inflammatory lesions are relatively uncommon compared to neoplastic lesions [10]. Thus far, only two publications have documented 13 canine cases of hypertrophic ganglioneuritis, diagnosed by MRI, which occur predominantly in large breeds [1,2]. These cases include nine Staffordshire Bull Terriers, one American Bulldog, one Labrador Retriever, one Cavalier King Charles Spaniel, and one Yorkshire Terrier, with Staffordshire Bull Terriers (9/13) being the most reported breed [1,2]. Only one report described unilateral C2 hypertrophic ganglioneuritis causing asymmetric spinal cord compression in a small-breed dog. A malignant PNST or lymphoma was considered likely owing to its unilateral presentation, but the histology confirmed it as hypertrophic ganglioneuritis [1].
One study reviewed the MRI findings of hypertrophic ganglioneuritis in 12 dogs. This condition typically manifests at the C2 level, showing symmetrical bilateral enlargement with strong contrast enhancement of the C2 spinal nerve roots. These hypertrophied nerve roots caused various degrees of spinal cord compression and distortion. Routine CSF analysis for cytology, protein concentration, and total nucleated cell counts was within the normal reference intervals for all dogs [2]. The similar MRI findings and CSF analysis result in this case suggested hypertrophic ganglioneuritis.
This study also found that all symptomatic cases of hypertrophic ganglioneuritis with neurological deficits, accounting for eight out of 12 dogs (66.7%), exhibited moderate to severe spinal cord compression. The remaining four dogs (33.3%) were clinically insignificant. Hence, mild spinal cord distortion or compression is defined as slight lateral shape changes. Moderate compression was noted, characterized by complete triangular distortion, with enlarged nerve rootlets measuring less than half the diameter of the cranial cervical spinal cord at the mid-body level of the atlas. Severe compression was characterized by irregular, narrowed shape change, where dorsal nerve rootlets were thicker than half the diameter of the normal cranial cervical spinal cord at the same level [2]. In the present case, moderate spinal cord compression was observed before treatment, which improved to mild compression on the follow-up MRI performed after immunosuppressive steroid therapy. This suggests a potential correlation between the clinical symptoms and MRI findings of spinal cord compression.
CIDP causes significant spinal cord compression because of bilaterally symmetrical nerve root enlargement. In human patients, CIDP is commonly treated with corticosteroids, intravenous immunoglobulins, plasma exchange, and azathioprine, leading to satisfactory improvement in most cases. CIDP can lead to severe disability if left untreated [11,12]. Five cases of C2 nerve root lesions in dogs showed clinical improvement after corticosteroid treatment [2]. In one case of unilateral chronic hypertrophic ganglioneuritis, however, there was no response to corticosteroids administered at an anti-inflammatory dose rather than an immunosuppressive dose [1].
In the present case, the patient was prescribed an immune-suppressive dose of prednisolone (1 mg/kg PO q12h), pregabalin (2 mg/kg PO q12h), and methocarbamol (15 mg/kg PO q12h) starting from the day of the MRI examination. The dog showed consistent gait improvement from the second day of medication, and treatment continued for approximately three months until the follow-up MRI. Unlike cases involving spinal nerve tumors, which often require invasive treatments such as surgery, radiation, or chemotherapy, the clinical condition improved with immunosuppressive steroid therapy alone, suggesting that the lesion was inflammatory rather than neoplastic. Nevertheless, the inability to perform a histopathology examination is the main limitation of this study.
In conclusion, this paper reports the MRI findings of bilaterally symmetrical enlargement of the C2 spinal nerve roots and significant T1 contrast enhancement in a dog, which strongly suggests hypertrophic ganglioneuritis. This case highlights the importance of follow-up MRI to assess treatment efficacy and enhance understanding of hypertrophic ganglioneuritis. Future studies should include histopathology confirmation to validate these diagnostic criteria and therapeutic outcomes.
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