NEUROMUSCULAR CASE OF THE MONTH - January 2005
Masticatory muscle myositis in a dog with
probable systemic lupus erythematosus.
Contributed by Dr. Tabitha Shanies
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.
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.
ECG: Occasional VPCs, sometimes in doublets
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)
Thoracic radiographs (3 views): Questionable cranial mediastinal mass
Abdominal ultrasound: Few small splenic nodules, bilateral nephropathy
Echocardiogram: No structural changes in the heart, no masses noted
Thoracic/mediastinal ultrasound: No mass
Buccal mucosal bleeding time: 1 minute, 40 seconds (reference 2-4
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
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
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.
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.
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.
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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