Clinical History
Immune-mediated hemolytic anemia  (IMHA) was diagnosed 2 months prior to presentation. Tick titers were negative except the dog was positive for Lyme natural exposure and vaccination. Treatment was initiated with immunosuppressive dosages of prednisone,  cyclosporine A (CsA; 5.4 mg/kg BID for 2 days then 4 mg/kg BID) and doxycycline. Approximately 1-2 weeks later the owners noted that the dog seemed weak in the pelvic limbs. Bloodwork showed elevated creatine kinase (CK; 17,390; reference 10-200 IU/L) and asparatate aminotransferase (AST 1088; reference 0-40 IU/L) activities. BUN, creatinine, and phosphorus concentrations were within the reference range with mildly decreased calcium (8.3; reference 8.9-11.2 mg/dl). The blood levels of CsA were dramatically elevated at 2652 ng/ml (therapeutic range 400-600 ng/ml). The dog was taken off the CsA and after 7 days the level was still elevated at 1756 ng/ml. While off the drug the owners noted that the dog was brighter and was better able to stand. Since the IMHA was not under control, the dog was given a decreased dose of CsA which resulted in worsening of clinical signs. The dog became more depressed, was anorexic, and was unable to empty the bladder. Cyclosporine was discontinued 4 days prior to referral to the Veterinary Medical Teaching Hospital. During this time, the dog became non-ambulatory and developed bilateral pelvic limb edema.

Physical and Neurological Examination
The dog was non-ambulatory with marked quadparesis and generalized muscle atrophy. Pitting edema was present in the pelvic limbs. Patellar reflexes were present but withdrawal reflexes were decreased in all four limbs. Mentation and cranial nerves were normal although there was a voice change. Anatomic localization was to the neuromuscular system. 

Diagnostic Testing
CBC – continued hemolysis
Serum Chemistry Profile – CK and AST within the reference range; BUN 67; Creatinine 0.5; calcium 9.2 (8.7-11.2 mg/dl); phosphorus 5.5 (2.5-7.9 mg/dl)
Urinalysis– specific gravity 1.021 with raging urinary tract infection involving pseudomonas and enterococcus
Cyclosporine level – 580 ng/ml
Antibody titers for Toxoplasma and Neospora – Negative
Acetylcholine receptor antibody titer – 0.02 nmol/l (canine reference <0.6 nmol/l)
Lumbosacral radiographs – end-plate sclerosis and minimal spondylosis interpreted as evidence of LS intervertebral disc disease
Electrophysiology – abnormal spontaneous electrical activity in the distal limb muscles with normal motor nerve conduction velocity

Muscle and Nerve Biopsy
There was marked generalized myofiber atrophy with the sarcoplasm in several fibers having a basophilic granular appearance. A very prominent abnormality was the presence of numerous, multifocal and large calcific deposits       (A, arrows). The deposits stained darkly orange with alizarin stain for calcium (B, arrows). No abnormalities were found in the peripheral nerve biopsy specimen.

Conclusion
Cyclosporine A, alone or as part of a multi-drug immunosuppressive therapy, has been reported as a cause of myopathy in humans (Breil and Chariot 1999; Guis et al 2003). Clinical signs include myalgia, muscle weakness, quadriplegia, and elevated serum CK concentrations. Clinical signs of myopathy tend to disappear spontaneously when treatment is discontinued and CK levels return to the normal range. When treatment with CsA is re-initiated, there is an associated rise in CK levels. Other therapies including prednisone can aggravate the myopathy. The mechanism of CsA myotoxicity is unknown (Breil and Chariot 1999), although mitochondrial dysfunction has been implicated. A similar pattern of clinical signs, decreasing CK levels following cessation of drug therapy, and worsening of clinical signs with re-initiation of the drug occurred in this dog. It is not known why the blood levels of CsA were so high with standard therapeutic dosages. One possibility was an abnormality of P-glycoprotein, which is involved in CsA metabolism. If the mdr1 gene was mutated, CsA would be absorbed to a higher degree than normal. MDR genotyping (mdr1 gene) was performed (Dr. Katrina Mealey, Veterinary Clinical Pharmacology Laboratory, Pullman, WA). No abnormalities were identified in the mdr1 gene. The ultimate cause of the dogs demise was uncontrollable hemolysis and autoagglutination.

References

Breil M, Chariot P (1999). Muscle disorders associated with cyclosporine treatment. Muscle Nerve 22:1631-1636.

Guis S, Mattei J-P, Liote F (2003). Drug-induced and toxic myopathies. Best Practice & Research Clinical Rheumatology 17:877-907.

Mealey KL (2004). Therapeutic implications of the MDR1 gene. J Vet Pharmacol Therap 27:257-264.

Veterinary Clinical Pharmacology Laboratory: www.vetmed.wsu.edu/depts-vcpl/