History

A 6-year-old 730.0-kg Belgian gelding was presented for evaluation of bilateral swelling of the caudal poll. The horse was acquired by his owners several weeks prior with no known history of trauma or injury. The swelling was present at the time of purchase, and neither a cause for nor the duration of the swelling was disclosed to the current owner. On presentation, the horse was bright, alert, and responsive with normal vital parameters. Physical examination noted a 30 X 15-cm firm, nonpainful, bilaterally symmetrical swelling of the neck dorsal to vertebrae C1-C3. The horse had normal head carriage, and there were no proprioceptive or cranial nerve deficits.

Bloodwork was submitted for evaluation. A single lateral projection of the cranial cervical region was performed (Figure 1).

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Right lateral cervical radiograph of a 6-year-old Belgian gelding with bilateral swelling of the caudal poll.

Citation: Journal of the American Veterinary Medical Association 262, 7; 10.2460/javma.24.03.0201

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Diagnostic Imaging Findings and Interpretation

Dorsal to the C1-C3 vertebrae, there were several ovoid, soft tissue opaque masses that had punctate mineral opaque foci outlining the peripheral margins (Figure 2). The masses varied in size and extended caudally beyond the field of view. The dorsal margin of the C2 spinous process was irregular and had patchy moth-eaten lysis and mild sclerosis. The radiographic findings were most consistent with cranial nuchal bursitis and secondary osteitis of the C2 vertebra.

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Same image as Figure 1. Notice the bulging dorsal cutaneous margins of the neck (white arrows). There are numerous punctate mineral opaque foci forming ovoid structures dorsal to the cranial cervical vertebrae (white arrowheads). The dorsal aspect of the spinous process of C2 is irregular with moth-eaten lysis and sclerosis (black arrowheads).

Citation: Journal of the American Veterinary Medical Association 262, 7; 10.2460/javma.24.03.0201

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The CBC showed a mild leukocytosis (WBC count, 13.7 X 10³ WBCs/µL; reference range, 5.2 X 10³ to 10.1 X 10³ WBCs/µL), characterized by a mild, mature neutrophilia (neutrophil count, 10.8 X 10³ neutrophils/µL; reference range, 2.7 X 10³ to 6.6 X 10³ neutrophils/µL), and a mildly elevated fibrinogen (800 mg/dL; reference range, 0 to 200 mg/dL). The chemistry panel showed a mild hyperproteinemia (8.2 g/dL; reference range, 5.4 to 7.0 g/dL), a mild hyperglobulinemia (5.3 g/dL; reference range, 2.3 to 3.8 g/dL), and moderately decreased iron (38 µg/dL; reference range, 95 to 207 µg/dL). These changes were interpreted as chronic inflammation.

Ultrasonography was performed to further assess the cervical soft tissues (Figure 3). Ultrasound revealed large, cavitated masses that extended to both the left and right sides of the dorsal neck spanning the region from the cranial aspect of C1 to the level of the C3-4 articular process joints. The masses each had a moderately thick (1.2-cm), irregular, hyperechoic capsule. There were several irregularly shaped and variably sized strands of hyperechoic material extending from the capsule towards the fluid-filled center. Additionally, there were innumerable punctate hyperechoic foci within the capsular margins and the hyperechoic strands (Figure 3). The hyperechoic foci were interpreted as mineral, which was consistent with the radiographic findings. No abnormality was detected in the nuchal ligament. The margins of the spinous process of C2 were irregular, consistent with the suspected osteitis. Ultrasound-guided aspiration of the fluid was obtained and submitted for cytology and culture.

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Ultrasound image of the same horse at the level of C2 in a transverse plane. The horse’s right is to the left of the image. The nuchal ligament is present at the top of the image (black asterisk) and the spinous process of C2 is below (white arrow). The nuchal bursa has multiple hyperechoic opaque foci (white arrowheads) and a thick capsule (black arrowheads) and is distended with anechoic fluid.

Citation: Journal of the American Veterinary Medical Association 262, 7; 10.2460/javma.24.03.0201

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Treatments and Outcome

Approximately 860 mL of turbid fluid was aspirated from the masses. The horse was started on oral minocycline (4 mg/kg, PO, q 12 h for 3 to 4 months) and phenylbutazone (2 mg/kg, PO, q 12 h) and received 1 g of ceftiofur injected into the bursa.

Lyme PCR was performed on the fluid aspirated from the nuchal bursa and was moderately positive, whereas the anaerobic bacterial culture returned no growth. The equine multiplex Lyme assay serology testing revealed positive titers for OspA and negative titers for OspC and OspF. This is consistent with another case report of nuchal bursitis caused by Lyme disease.¹ The horse was discharged to the care of the owners. At the 2-week follow-up, the swelling remained but the horse was doing well and was comfortable.

Comments

The nuchal ligament is composed of organized, linear fibers made up of collagen and elastin, and it assists to passively elevate the head and neck of the horse through its elastic properties.² Associated with the ligament near its cranial insertion point is the cranial nuchal bursa, located just dorsal to the atlas (C1 vertebrae).³ Inflammation of this bursa typically presents as head and neck pain, swelling over the poll, and may include associated draining tracts.⁴ Cranial nuchal bursitis is colloquially referred to as “poll evil,” a name that encompasses a clinical presentation with different etiologies.¹ Other differential diagnoses for potential causes of swelling and pain at this region include cervical vertebrae fractures or dislocations and insertional desmopathies.²

Imaging plays a key role in the clinical workup of suspected nuchal ligament desmopathy and bursitis. Radiographs are frequently employed as a first line of investigation to evaluate swelling as it is readily available for most general practitioners. They are valuable in ruling out differential diagnoses with skeletal components, such as cervical vertebrae fractures. Ultrasound is the most sensitive, whereas CT and MRI are the most precise.² On ultrasound, edema associated with bursitis can be visualized, often as synovial proliferation and anechoic or echogenic fluid distension,¹ similar to this case.

Equine Lyme disease is not often implicated in the disease process of nuchal bursitis. The 3 clinical syndromes typically associated with equine Lyme disease are neuroborreliosis, uveitis, and cutaneous pseudolymphoma.¹ Only 1 previous case of Borrelia burgdorferi involved in equine nuchal bursitis has been documented and was similarly diagnosed with positive OspA antibodies against B burgdorferi on equine multiplex Lyme assay and positive Lyme PCR on bursal fluid samples.¹

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.