Physical and Neurological Examination

Abnormalities were limited to the neurologic examination. The cat was unwilling to walk more than a few steps (See video clip). The pelvic limbs showed significant weakness and spinal reflexes were diminished.  Conscious proprioception was normal in all four limbs. Hopping was diminished in the pelvic limbs. Wheelbarrowing was normal for a few steps, then the cat would collapse. Subjectively, there was significant pain in the lumbar and thoracic spine, and pain evident upon palpation of the pelvic and thoracic limb musculature. The cranial nerve examination was normal. The neuroanatomic localization was to the neuromuscular system (motor unit), although a diffuse spinal cord disease could not be ruled out based on the spinal pain.

Diagnostic Testing

CBC and serum chemistry profiles -normal

Serum creatine kinase concentration – 925 U/L (reference <314 U/L)

Serum antibody titer for Toxoplasma gondii – negative 

At this time treatment with clindamycin was initiated at 1.2 ml PO twice daily (25 mg/ml) for a total of 20 ml. The cat showed minimal improvement with antibiotic therapy and worsened 2 weeks later. The cat was again evaluated, and there was generalized weakness, some muscle pain, and an unwillingness to walk. Further diagnostics were performed.

Electrodiagnostic Testing

The electromyogram was abnormal with moderate spontaneous activity in all muscles tested (including limb and epaxial musles), consistent with either a myopathy or neuropathy (Go to video clip).The sciatic motor nerve conduction velocity was normal with a normal waveform.

Muscle and Nerve Biopsies

A biopsy from the semimembranous muscle was evaluated in frozen sections. There was moderate myofiber atrophy in a pattern consistent with denervation. Depletion of myelinated fibers and accumulation of myelin debris within intramuscular nerve branches (arrow) was evident (Fig. 1A). A control intramuscular nerve branch (arrow) shows the normal myelin staining pattern with the modified Gomori Trichrome stain in frozen muscle sections  (Fig. 1B). No abnormalities were identified in the biopsy from the peroneal nerve (Fig. 1C).

Fig1A. Patient

Fig1B. Control

Fig1C. Patient

Treatment and Clinical Outcome

A diagnosis of distal denervation was made based on depletion of myelinated nerve fibers within intramuscular nerve branches, normal peroneal nerve biopsy, and an absence of a primary myopathy within muscle fibers. Treatment was initiated with prednisone (5 mg daily) until biopsy results were available. The cat showed significant improvement with a gradual increase in muscle strength (Go to video clip). Over the next 3-4 months the prednisone was slowly tapered. Eight months later there was a relapse with the cat again only weakly ambulatory. Spinal reflexes were reduced. No cranial nerve abnormalities were noted. Electromyography again showed moderate spontaneous activity in all muscles tested (limb and epaxial) with a normal motor nerve conduction velocity. Treatment was initiated with immunosuppressive dosages of prednisone with no significant improvement. The dose of prednisone was increased to 15 mg daily and chlorambucil was added at 0.2 mg/kg PO q 48hr.  Following clinical improvement the prednisone dosage was decreased to 7.5 mg daily. When the dosage of chlorambucil was decreased clinical signs again returned. The original dosage of chlorambucil was restarted and the cat is continuing to do well a little over 2 years after initial evaluation.