NEUROMUSCULAR CASE OF THE MONTH – JANUARY 2009

Generalized weakness and profound hypothyroidism in a 5 year old male (neutered) Cocker Spaniel
Contributed by Drs. Ronald Lyman, Robert Runde and M. Angela Murphy
Animal Emergency & Referral Center
Ft. Pierce, FL

Clinical History
A 5 year old male (neutered) Cocker spaniel was referred for evaluation of a chronic history of head bobbing and weakness on exercise, with recent dark tarry stools and poor appetite.  A “tragic expression” was present on the dog’s face (see image below).

cockerspaniel

Physical and Neurological Examination
The dog was aware of surroundings but appeared depressed. The gums were pale. On gait analysis, the dog was weak and would only walk a few steps before stopping (Go to Video Clip).  Cranial nerve function and spinal reflexes were normal.  A Tensilon test was negative.  A neuromuscular disorder, possibly secondary to an underlying systemic disease, was suspected.

Diagnostic Testing
CBC – PCV 31 (37.0-55.0%), HgB 10 (12-18 g/dl)
Direct Coombs – Positive at 1:4 (reference negative)
Serum Chemistry Profile – Cholesterol 386 (110-320 mg/dl), Creatine Kinase 228 (10-200 U/L)
Acetylcholine receptor antibody – 0.02 (canine reference <0.6 nmol/l)

Thyroid Evaluation – T4 <0.2 (1.0-4.0 µg/dl, Free T4 by equilibrium dialysis <2 (6-40 pmol/L), TSH 0.89 (0.0-0.60 ng/ml).  An elevated TSH concentration with low or low-normal T4  or free T4 concentration is consistent with primary hypothyroidism.

Muscle biopsies – Marked type 2 fiber atrophy and type 1 fiber predominance were identified  within the muscle biopsy sections consistent with an endocrine disorder such as hypothyroidism  (Figure A,B).  In Fig. A (ATPase reaction at pH 9.8) type 1 fibers are light  and type  2  fibers are dark. In Fig. B (ATPase reaction at pH 4.3) type 1 fibers are dark and type 2 fibers are light or intermediate (type 2C). Numerous nemaline rod bodies (Fig. C, modified Gomori trichrome stain) and glycogen or polysaccharide deposits (Fig. D, PAS stain) were present which can also be found in chronic hypothyroidism.

ARPase
Figure A

 

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Figure B

 

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Figure C
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Figure D

Intestinal and liver biopsies – Chronic lymphocytic-plasmacytic inflammatory bowel disease and diffuse hydropic vacuolar degeneration of hepatocytes.

Muscle Carnitine Quantification –
Carnitine Total – 6.8 (12-41 nmol/mg protein)
Free Carnitine – 3.1 (11-33 nmol/mg  protein)
Esters Carnitine – 3.7 (nmol/mg protein)
Ester/Free Ratio – 1.19

Diagnosis and Outcome
Hypothyroidism and Coombs positive anemia were consistent with multi-systemic immune-mediated disease.  Pathologic changes found in the muscle, and low total and free muscle carnitine levels, have been previously identified in cases of canine hypothyroid myopathy, and most recently, described in an experimental model of canine hypothyroidism (Rossmeisl et al, Am J Vet Res 2009, in press).  There are many similarities to this case and the November 2006 Case of the Month. The dog initially responded well to thyroid and carnitine supplementation, and treatment for other concurrent problems with return of muscle strength. However, the dog presented one month later for complications resulting from other related clinical problems and was euthanized.

 

 

 

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