NEUROMUSCULAR CASE OF THE MONTH - SEPTEMBER 2015From the 2006 Archives: Malignant peripheral nerve sheath tumor in a 5 year old MC Standard
Contributed by Dr.Beatrix Nanai and Dr.
Animal Emergency & Referral Center
Ft.Pierce, FL 34982
The dog presented with a 10 day history of left thoracic
Physical and Neurological Examination
On initial presentation the dog showed left thoracic limb
lower motor neuron paraparesis, although
the dog was weight bearing and could advance the limb. Severe atrophy
of the infraspinatus and supraspinatus muscles was noted with the remainder of the musculature normal in
appearance. There was moderate
caudal cervical hyperesthesia. No
mass or swelling could be palpated in the axillary area.
CBC and chemistry panels – No abnormalities
Abdominal, thoracic and spinal radiographs – No abnormalities
Myelogram – Very mild ventral extradural compressions at C5-6, C6-7
Electromyography – Positive sharp
waves and fibrillation potentials focally in the left supraspinatus and infraspinatus muscles (Fig. 1A). All other muscles evaluated were normal. The
motor nerve conduction velocity could not be measured on the left
MRI – Hyperintensity on T2 at the level of C7 showing an enlarged nerve root (Fig. 1B)
A peripheral nerve sheath tumor was suspected. The owner declined amputation at that time and treatment with gabapentin (10 mg/kg TID), piroxicam (0.3 mg/kg SID), and omeprazole (1 mg/kg SID) was initiated.
Second Presentation 3 weeks
The dog was represented 3 weeks
later and was non-weight bearing (Fig. 1C). Muscle atrophy was more pronounced (Fig. 1D) and affected
all of the left thoracic limb muscles including the biceps and triceps
muscles. The dog was unable to advance the limb. There was still
no evidence of swelling or pain in the axillary region. At this time the owner requested amputation
The left thoracic limb including the scapula was amputated
and a hemilaminectomy performed
at C6-7.The C7 nerve root appeared of appropriate size within
the spinal canal but was thick and firm directly outside the
spinal canal. Histopathology at the time of amputation showed
active denervation within the muscle
biopsies and severe nerve fiber loss, cellular infiltration,
and foci of lymphocytic infiltration
within the subscapular nerve (Fig. 2A,B). Differentials
at this time included malignant peripheral nerve sheath tumor
or, due to the amount of lymphocytic infiltration, a hypertrophic neuritis. A second opinion at that time confirmed
a malignant peripheral nerve sheath tumor (Dr. Brian Summers).
Most peripheral nervous system tumors in the dog are malignant
and undifferentiated, and are best designated malignant peripheral
nerve sheath tumors without specification of the tumor type.
These tumors usually have a bad prognosis as they commonly
extend into the vertebral canal or the thorax. Approximately
3 months after surgery the dog developed a left Horner’s syndrome
and cervical hyperesthesia. One month later, a large mass
was evident at the former surgery site. The dog was euthanized.
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