Tongue Atrophy in 5 Year-Old Female Spayed Pembroke Welsh Corgi

Clinical History

Non-progressive mild atrophy of the temporalis muscles was noted 2 years prior without obvious jaw pain or restricted jaw mobility. Two months prior to presentation, the owner noted the right side of the tongue rolling inward progressing to rostral tongue atrophy and paralysis. The paralysis progressed to involvement of the entire tongue with moderate difficulty eating and drinking. The tip of the tongue folded over as shown in the images below. The pet was otherwise healthy.

Physical and Neurological Examination

Mild atrophy of the masticatory muscles was observed with decreased motor function to the rostral 3 cm of the tongue. The gag reflex was considered normal and no other deficits were noted. The remainder of the physical and neurological examinations was unremarkable. Sedated oral examination revealed no masses or gross abnormalities besides the rostral tongue atrophy. A biopsy was obtained from the tongue that showed marked myofiber atrophy with mild lymphoplasmacytic myositis.

Diagnostic Tests

DCBC: WNL
Chemistry analysis including creatine kinase activity: WNL
Urinalysis: RBCs 11-20/hpf, otherwise no specific findings
T4/Free T4: Within reference range
Fecal: Negative
Tick PCR panel: All negative

At this time treatment was started with Doxycycline 50mg PO BID and Clindamycin 75mg PO BID. No improvement was noted on antibiotics and the pet was referred to a board certified neurologist.

Further Diagnostics by Neurologist

Results of neurologic examination were similar to noted above with rostral tongue atrophy and paralysis. Electromyographic examination and repeat muscle biopsies were recommended. Marked spontaneous activity including fibrillation potentials and positive sharp waves was present in all areas of the tongue and to a lesser degree in the masticatory muscles. Mild spontaneous activity was also noted in isolated thoracic and pelvic limb muscles with a patchy distribution.
Muscle biopsies were collected from the tongue (rostral and caudal), temporalis and triceps muscles. Marked generalized myofiber atrophy, endomysial fibrosis and scattered mixed mononuclear cell infiltrations were present in the rostral and caudal tongue biopsies (see images below, H&E stain 10X on the left and 20X on the right). Multifocal areas of mild to moderate lymphocytic infiltrations were present in the temporalis muscle. A single focus of lymphocytic infiltration was observed in the triceps muscle. Immunophenotyping was performed using a panel of antibodies against canine lymphocyte antigens. The predominant cell type was CD8+ T lymphocytes with lesser numbers of CD4+ T lymphocytes and only rare B lymphocytes.

Conclusion

The clinical presentation, electrodiagnostic findings and muscle histopathology are consistent with the atypical polymyositis previously reported in a Pembroke Welsh Corgi (Ito D et al. Symptomatic tongue atrophy due to atypical polymyositis in a Pembroke Welsh Corgi. J Vet Med Sci 2009;71:1063-1067). Treatment was initiated with oral prednisone (5 mg twice daily) and cyclosporine (50 mg twice daily). Cyclosporine levels will be monitored and tapered to lowest effective dose.