NEUROMUSCULAR CASE OF THE MONTH - January 2005

Masticatory muscle myositis in a dog with probable systemic lupus erythematosus.
Contributed by Dr. Tabitha Shanies
Cornell University
Ithaca, NY


Clinical History
An 8 year old female spayed mixed breed dog was presented for a two week history of inappetance progressing to anorexia and adipsia, difficulty walking, and increased respiratory effort. A fever had been documented (104.3° F). Routine bloodwork, including a heartworm test, was negative. The dog was treated with cephalexin and aminophylline for possible bronchitis, and deracoxib for presumed discomfort. The clinical condition worsened prompting referral.

Physical Examination
The dog was depressed, mildly febrile (102.8° F), had a small amount of serosanguinous nasal and oral discharge, severe halitosis, and foamy, sticky saliva. The jaw could not be opened (Fig. 1) and the masticatory muscles were firm and possibly painful on palpation. The dog panted with a closed mouth. An occasional dropped beat was found on cardiac auscultation, but thoracic auscultation was otherwise normal. All palpable joints were swollen. A left sided epistaxis developed 48 hours into the hospital stay.


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Figure 1.

Diagnostic Testing

ECG: Occasional VPCs, sometimes in doublets or triplets
Pulse oximetry: 100% on room air
CBC:  Low normal hematocrit (HCT), neutrophilia with left shift and toxic neutrophils, mild thrombocytopenia
Serum chemistry: Mild hyperglobulinemia and hypoalbuminemia, moderate elevation of liver and muscle enzymes (ALT, AST, ALP, CK), mild hyperbilirubinemia
Urinalysis: 1+ proteinuria, 5-20 RBC/hpf (voided sample)
ANA: Negative
Thoracic radiographs (3 views): Questionable cranial mediastinal mass
Neck/skull radiographs: Normal
Abdominal ultrasound: Few small splenic nodules, bilateral nephropathy
Echocardiogram: No structural changes in the heart, no masses noted
Thoracic/mediastinal ultrasound: No mass found
Buccal mucosal bleeding time: 1 minute, 40 seconds (reference 2-4 minutes)
CT head and nasal passages: Fluid filled left nasal passages, no bony changes or mass effect
Joint fluid cytology (multiple joints): Sterile suppurative inflammation
Joint fluid culture (multiple joints): No bacterial growth
Muscle biopsy temporalis: Inflammatory myopathy/masticatory muscle myositis (Fig. 2)
2M antibody titer: Positive at 1:500
Coagulation profile: High normal prothrombin time/activated partial thromboplastin time, prolonged thrombin clotting time, elevated fibrinogen, markedly elevated D-dimers, normal antithrombin III
Antibody titers for infectious agents: Negative for Lyme, Ehrlichia canis, Ehrlichia risticii, Ehrlichia equi, Rocky Mountain Spotted Fever, Bartonella, Toxoplasma and Neospora. A low positive antibody titer (1:100) was found for L. canicola and L. autumnalis which was unchanged when tested 1 week later.

Diagnosis and Initial Treatment
A presumptive diagnosis of systemic lupus erythematosus (SLE) was made based on the presence of immune-mediated joint and muscle disease. As coagulation tests did not disclose a primary coagulopathy and masses were not found in the nasal passages by CT, an immune-mediated rhinitis was also considered possible. Treatment during hospitalization included supportive care, temporary tracheostomy, syringe feedings, dexamethasone Sodium phosphate, antibiotics, and famotidine. Since epistaxis became bilateral, a fresh frozen plasma transfusion was administered for possible disseminated intravascular coagulopathy. Desmopressin was given for possible occult thrombocytopathia, intra-nasal epinephrine was administered to slow bleeding, and a packed red blood cell transfusion was given due to progressive blood loss and anemia.

Clinical Course
During the course of hospitalization, epistaxis ceased and range of motion of the jaw improved. Repeated bloodwork prior to discharge showed normal platelet count, stabilization of the HCT, resolution of toxic changes, normal albumin and globulin, normal ALT, AST, CK, and bilirubin, and mildly elevated ALP (likely referable to steroid therapy). The dog was discharged on oral prednisone (1 mg/kg BID), famotidine for gastroprotection, mini-dose aspirin (0.5 mg/kg/day) to combat pro-thrombotic tendencies, and Cosequin. Plans were to institute azathioprine therapy once range of jaw motion further improved, as all medications prescribed had to be crushed and administered via syringe, (which would result in an unacceptable level of human exposure to azathioprine).

The dog initially did well at home with an improved activity level, gradually increasing jaw mobility, as well as some ability to eat softened foods without syringe assistance. However, 10 days after discharge, the dog represented on emergency for an acute onset of inability to stand, vomiting and bloody diarrhea, a cold right thoracic limb, poor pulses in the left pelvic limb, ecchymotic hemorrhages on the ventral abdomen, bilateral scleral hemorrhages, significant masticatory muscle atrophy (Fig. 3), abnormal mentation, positional vertical nystagmus, absent menace response OD, and bilateral nasal hypalgesia. Azostix testing revealed azotemia (BUN 50-80 mg/dl). Based on the presumptive diagnosis of multifocal thromboembolic disease, euthanasia was elected.


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1 Figure 3.


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Necropsy
Multifocal thrombi (multiple renal, right brachial artery, right femoral vein, spleen) and an irregularly shaped leaf-like cystic mass in the cranial mediastinum were identified on gross necropsy. Histopathology revealed renal, splenic, lingual, cardiac, and brain infarctions, steroid hepatopathy, and severe right sided brachial arteritis. The cranial mediastinal mass was composed of thymic remnant tissue as well as a thymic brachial cyst.


Conclusion
Clinical findings in this case are consistent with a diagnosis of SLE and a subsequent pro-thrombotic state. Although there is one report in the literature of autoimmune disease in a dog with a thymic branchial cyst, this association is likely coincidental.

 

References

Marks SL, Henry CJ. CVT Update: Diagnosis and treatment of systemic lupus erythematosus. In: Bonagura JD, ed: Current Veterinary Therapy XIII: Small Animal Practice, WB Saunders 2000; pp 514-516.

Day MJ. Review of thymic pathology in 30 cats and 36 dogs. Journal of Small Animal Practice 1997;38:393-403.

Jones DR. Canine systemic lupus erythematosus: new insights and their implications. Journal of Comparative Pathology 1993;108:215-228.



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