Myotonia associated with hyperadrenocorticism in two dogs

Trismus due to myotonia associated with hyperadrenocorticism in a dog

We present the report of trismus due to hyperadrenocorticism-associated myotonia diagnosed by electromyography in a dog. An intact female Miniature Dachshund, 13 years and 9 months old, presented with stiff gait and trismus as well as polyuria and polydipsia. Abdominal ultrasonography showed enlarged adrenal glands. An adrenocorticotropic hormone stimulation test revealed an exaggerated response. Based on these findings, this case was diagnosed with hyperadrenocorticism. Electromyography revealed myotonic discharge in the temporalis muscle and limbs. Therefore, trismus was considered to be caused by hyperadrenocorticism-associated myotonia, and the case was treated with oral trilostane (1.3 mg/kg, once daily). During the 4-month follow-up period, despite the partial improvement in stiff gait, trismus did not recover. Long-term data on more cases are warranted to assess the prognosis and clinical characteristics of trismus due to hyperadrenocorticism-associated myotonia.

Clinical features of muscle stiffness in 37 dogs with concurrent naturally occurring hypercortisolism

BACKGROUND

Severe muscle stiffness (SMS) in dogs with hypercortisolism (HC) is uncommon.

OBJECTIVES

To evaluate signalment, presentation, treatments, and long-term outcomes of dogs with concurrent HC and SMS.

ANIMALS

Thirty-seven dogs.

METHODS

Medical records of dogs with HC and concurrent SMS were recruited from 10 institutions. Clinical information, test results, therapeutic responses, and survival times were reviewed.

RESULTS

All 37 dogs with HC and SMS had pituitary-dependent hypercortisolism (PDH); 36/37 weighed <20 kg. Signs and test results were typical of PDH aside from SMS, initially diagnosed in all 4 limbs in 9, pelvic limbs of 22, and thoracic limbs of 6 dogs. Hypercortisolism and SMS were diagnosed together in 3 dogs; HC 1-36 months before SMS in 23; SMS 1-12 months before HC in 11. Mitotane or trilostane, given to control HC in 36/37 dogs, improved or resolved HC signs in 28; SMS did not resolve, remaining static or worsening in 31/36 dogs, mildly improving in 5/19 dogs given additional therapies. Progression of SMS included additional limbs in 10 dogs and the masticatory muscles of 2. The median survival time from diagnosis of SMS was 965 days (range, 8-1188).

CONCLUSIONS AND CLINICAL IMPORTANCE

Concurrent SMS and HC is uncommon, possibly affecting only dogs with PDH. Development of SMS might occur before or after diagnosis of HC. Apart from SMS, the clinical picture and survival time of these dogs seem indistinguishable from those of dogs with HC in general. However, while muscle weakness usually resolves with HC treatment SMS does not.

Quantitative assessment of muscle mass and gene expression analysis in dogs with glucocorticoid-induced muscle atrophy

The present study aimed to quantitatively evaluate muscle mass and gene expression in dogs with glucocorticoid-induced muscle atrophy. Five healthy beagles received oral prednisolone for 4 weeks (1 mg/kg/day), and muscle mass was then evaluated via computed tomography. Histological and gene expression analyses were performed using biopsy samples from the biceps femoris before and after prednisolone administration. The cross-sectional area of the third lumbar paraspinal and mid-femoral muscles significantly decreased after glucocorticoid administration (from 27.5 ± 1.9 to 22.6 ± 2.0 cm² and from 55.1 ± 4.7 to 50.7 ± 4.1 cm², respectively; P<0.01). The fast- and slow-twitch muscle fibers were both atrophied (from 2,779 ± 369 to 1,581 ± 207 μm² and from 2,871 ± 211 to 1,971 ± 169 μm², respectively; P<0.05). The expression of the growth factor receptor-bound protein 10 (GRB10) significantly increased after prednisolone administration (P<0.05). Because GRB10 suppresses insulin signaling and the subsequent mammalian target of rapamycin complex 1 activity, increased expression of GRB10 may have resulted in a decrease in protein anabolism. Taken together, 1 mg/kg/day oral prednisolone for 4 weeks induced significant muscle atrophy in dogs, and GRB10 might participate in the pathology of glucocorticoid-induced muscle atrophy in canines.

Diagnosis of spontaneous canine hyperadrenocorticism: 2012 ACVIM consensus statement (small animal)

This report offers a consensus opinion on the diagnosis of spontaneous canine hyperadrenocorticism. The possibility that a patient has hyperadrenocorticism is based on the history and physical examination. Endocrine tests should be performed only when clinical signs consistent with HAC are present. None of the biochemical screening or differentiating tests for hyperadrenocorticism are perfect. Imaging can also play a role. Awareness of hyperadrenocorticism has heightened over time. Thus, case presentation is more subtle. Due to the changes in manifestations as well as test technology the Panel believes that references ranges should be reestablished. The role of cortisol precursors and sex hormones in causing a syndrome of occult hyperadrenocorticism remains unclear.

Confirmed 2,4-dichlorophenoxyacetic acid toxicosis in a dog

A 2-year-old, intact male Weimaraner was evaluated for episodic extensor rigidity and a stiff gait of 24 hours' duration. Percussion of the proximal appendicular muscles with a reflex hammer resulted in formation of dimples consistent with myotonia. Electromyography identified myotonic potentials. Residues of 2,4-dichlorophenoxyacetic acid (2,4-D) were detected in both serum and urine. The dog was treated with intravenous fluid therapy for 36 hours, and clinical signs improved dramatically. Toxicosis with 2,4-D should be considered a differential for acquired myotonia in dogs with or without systemic signs. Exposed dogs with only clinical signs of myotonia can have good clinical outcomes. A confirmed clinical case of 2,4-D toxicosis in the dog has not previously been reported.

Myotonia and disorders of altered muscle cell membrane excitability

Altered excitability of the skeletal muscle membrane (sarcolemma) can result in clinical signs of muscle dysfunction. Hyperexcitability of the sarcolemma results in myotonia, and hypoexcitability results in paresis or paralysis. Our understanding of the physiologic and molecular bases of disorders of sarcolemmal excitability is rapidly increasing as techniques for evaluation are improved. This article reviews muscle excitability disorders in dogs and cats and their pathogenesis.