CASE DESCRIPTION A 5-year-old castrated male Maltese was evaluated for intermittent clinical signs of muscle cramping and abnormal movements of the skin of the right pelvic limb at the site where an infiltrative lipoma had twice been resected. After the second surgery, the surgical field was treated with radiation therapy (RT). The clinical signs developed approximately 14 months after completion of RT.
CLINICAL FINDINGS When clinical signs were present, the right biceps femoris and semitendinosus muscles in the area that received RT were firm and had frequently visible contractions, and the skin overlying those muscles had episodic vermiform movements. Electromyography of those muscles revealed abnormal spontaneous activity with characteristics consistent with myokymic discharges and neuromyotonia. Magnetic resonance imaging of the affected leg revealed no evidence of tumor regrowth. The myokymia and neuromyotonia were considered secondary to RT.
TREATMENT AND OUTCOME 4 U of Clostridium botulinum toxin type A (BoNT-A) neurotoxin complex was injected into the affected muscles at each of 6 sites twice during a 24-hour period (ie, 48 U of BoNT-A were administered). The clinical signs were completely resolved 10 days after BoNT-A treatment and were controlled by repeated BoNT-A treatment every 3 to 4 months for > 1 year.
CLINICAL RELEVANCE To our knowledge, this is the first report of myokymia and neuromyotonia secondary to RT in a dog. For the dog of this report, injection of BoNT-A into the affected muscles was safe, effective, and easy to perform.
To determine whether dogs have a meningovertebral ligament (MVL) and to assess the effect that structure may have on pathological lesions within the ventral epidural space.
Cadaveric specimens from 6 neurologically normal dogs and 2 dogs with vertebral neoplasms that extended into the epidural space and MRI sequences and cytologic preparations from 2 dogs with compressive hydrated nucleus pulposus extrusion that underwent decompressive surgery.
The vertebral column was removed for gross and histologic examination from the cadavers of neurologically normal dogs and dogs with vertebral neoplasms. For dogs with hydrated nucleus pulposus extrusion, MRI sequences to assess lesion location and topography and cytologic preparations of material surgically extirpated from the ventral epidural space were reviewed.
All dogs had an MVL, which formed the ventral boundary of the epidural space and consisted of fibrous bands that attached the external ventral surface of the dura mater of the spinal cord to the dorsal surface of the vertebral bodies throughout the length of the vertebral canal. Both vertebral neoplasms had a bilobed appearance as did the extruded nucleus pulposus lesions on MRI sequences.
CONCLUSIONS AND CLINICAL RELEVANCE
Results of the present study indicated that dogs have an MVL, which creates an anatomic barrier within the ventral epidural space and causes pathological lesions to adopt a bilobed shape regardless of the pathogenic process. Further anatomic studies of the MVL and vertebral canal of dogs are necessary to elucidate how those structures affect lesion progression within the ventral epidural space.