Routine and specialized laboratory testing for the diagnosis of neuromuscular diseases in dogs and cats

Successful Emergency Management of a Dog with Ventilator-Dependent Acquired Myasthenia Gravis with Immunoadsorption

A one-year-old, female intact Samoyed, 12.5 kg, was presented with coughing for 2 weeks, progressive appendicular and axial muscle weakness, megaesophagus and labored breathing for 5 days. There was no improvement with standard treatment. Acquired myasthenia gravis was suspected and the dog was referred with increasing dyspnea. At presentation, the dog showed a severely reduced general condition, was non-ambulatory and showed abdominal and severely labored breathing. A marked hypercapnia (PvCO2 = 90.1 mmHg) was present in venous blood gas analysis. The serum anti-acetylcholine receptor antibody test was consistent with acquired myasthenia gravis (2.1 nmol/L). The dog was anesthetized with propofol and mechanically ventilated with a Hamilton C1 ventilator. Immunoadsorption was performed with the COM.TEC® and ADAsorb® platforms and a LIGASORB® adsorber to eliminate anti-acetylcholine receptor antibodies. Local anticoagulation was performed with citrate. Treatment time for immunoadsorption was 1.5 h with a blood flow of 50 mL/min. A total plasma volume of 1.2 L was processed. Further medical treatment included intravenous fluid therapy, maropitant, esomeprazole, antibiotic therapy for aspiration pneumonia and neostigmine 0.04 mg/kg intramuscularly every 6 h for treatment of acquired myasthenia gravis. Mechanical ventilation was stopped after 12 h. A percutaneous gastric feeding tube was inserted under endoscopic control on day 2 for further medical treatment and nutrition. A second treatment with immunoadsorption was performed on day 3. Again, a total plasma volume of 1.2 L was processed. Immediately after this procedure, the dog regained muscle strength and was able to stand and to walk. After 6 days, the dog was discharged from the hospital. This is the first report of immunoadsorption for emergency management of a dog with acute-fulminant acquired myasthenia gravis. Immunoadsorption may be an additional option for emergency treatment in dogs with severe signs of acquired myasthenia gravis.

Clinical enzymology of the dog and cat

Clinical enzymology studies the enzyme activity in serum or other body fluids for the diagnosis, prognosis or monitoring of a variety of diseases. Clinical enzymology has greatly benefited from advances in technology and is now an integral part of laboratory analysis. However, to maximise the clinical benefits of serum enzyme measurement, clinicians and clinical pathologists must have a good understanding of the pathophysiology behind serum enzyme alterations. They must also be aware of the preanalytical and analytical factors that can affect the accuracy of serum enzyme activity measurement. This review article first covers the basic concepts of clinical enzymology and the general mechanisms related to serum enzyme alterations. Then, the review discusses the potential effects of various preanalytical and analytical factors on enzyme activity measurement. Lastly, it explores the pathophysiology and clinical use of various serum enzymes in canine and feline medicine. The present review article aims to be a comprehensive one-stop source for clinical pathologists and small animal practitioners.

Seronegative Myasthenia Gravis with Concomitant SARS-CoV-2 Infection in a Dog

Myasthenia gravis (MG) is a disorder of neuromuscular transmission affecting the neuromuscular junction. The majority of cases involve an autoimmune attack against AChR, but a limited number of patients are seronegative for AChR antibodies. Viral infection is incriminated as a trigger for MG occurrence, and in a limited number of reports, infection with SARS-CoV-2 was found to be associated with MG expression in humans. In this report, we describe case of seronegative generalized MG in a 2-year-old crossbred female dog associated with SARS-CoV-2 infection due to close exposure to an infected owner.

Case Report: Persistent Moderate-to-Severe Creatine Kinase Enzyme Activity Elevation in a Subclinical Dog

A 4-year-old, male-castrated, mixed breed dog was presented for a routine wellness examination at which time a moderate increase in serum creatine kinase (CK) enzyme activity (hyperCKemia) (15,137 IU/L; reference interval 10–200 IU/L), and moderate increases in alanine transaminase and aspartate aminotransferase enzyme activities were first identified. There was no history of clinical abnormalities (e.g., lethargy, lameness, anorexia, dysphagia, weakness, gait abnormalities, or exercise intolerance) and the physical examination was unremarkable. The dog was screened for several relevant potential infectious diseases known to cause inflammatory myopathies and was treated empirically with clindamycin. The serum total CK enzyme activity remained increased, which prompted recommendations for an echocardiogram, electromyogram (EMG), and muscle biopsy acquisition. The echocardiogram and electrocardiographic monitoring were unremarkable. The EMG and muscle biopsies were declined by the owner. The dog was evaluated several times in the subsequent 5 years and remained subclinical with unremarkable physical examinations despite a persistent moderate-to-severe hyperCKemia. Differential diagnoses considered most likely in this dog were an occult/latent hereditary muscular dystrophic disorder or idiopathic hyperCKemia, a phenomenon not yet reported in the veterinary literature. This report describes for the first time, clinical and diagnostic features of a subclinical dog with persistent moderate-to-severe hyperCKemia.

Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Background

Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited.

Hypothesis/Objectives

Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long‐term prognosis and low rates of remission.

Animals

Ninety‐four client‐owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States.

Methods

Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission.

Results

An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4‐40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0‐23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8‐35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5‐38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age (P = .04) and comorbid endocrine disease (P = .04) were associated with clinical remission. Initial AChR Ab concentration (P = .02) and regurgitation (P = .04) were negatively associated with clinical remission.

Conclusions and Clinical Importance

Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.

Progressive increases in creatine kinase activity in an anorexic cat with necrotising myopathy

Case summary

A 5-year-old castrated male domestic shorthair cat with weight loss and reduced appetite was evaluated for increased and progressively rising creatine kinase (CK) activity. The cat had recently been diagnosed with hepatic lipidosis. Muscle biopsy and histopathology revealed mild myonecrosis and phagocytosis without obvious inflammatory cell infiltrates. Resolution of necrotising myopathy was observed after a short course of anti-inflammatory prednisolone and nutritional supplementation.

Relevance and novel information

This is the first report of a necrotising myopathy in a cat associated with progressively increasing CK activity and decreased appetite. Anorexia in cats has been associated with increased CK activity, but an underlying cause of this CK elevation has only been postulated. Here we document muscle necrosis and muscle stiffness in a cat with anorexia.

Therapeutic plasma exchange as adjunct therapy in 3 dogs with myasthenia gravis and myasthenia-like syndrome

OBJECTIVE

To describe the use of therapeutic membrane-based plasma exchange (TPE) for treatment of clinical signs associated with suspected acquired myasthenia gravis (MG) in 3 dogs.

CASE SERIES SUMMARY

Three dogs presented with clinical signs consistent with acquired MG. All 3 dogs were medically managed prior to being treated with TPE. Two of the 3 dogs had increased acetylcholine receptor antibody titers that decreased after TPE. One dog diagnosed with primary MG became clinically normal after 2 sessions of TPE and continued to do well with medical management several months later. The second dog was diagnosed with a suspect thymoma, and TPE was performed as a bridge to surgery, with marked improvement of clinical signs after TPE. The dog was ultimately diagnosed with a thymic carcinoma. The third dog had a positive acetylcholine antibody titer and was ultimately diagnosed with hemangiosarcoma (spleen and liver) and invasive mediastinal thymoma. This dog developed severe pneumonia, was ventilator dependent, and died of multiple organ dysfunction. No immediate complications were observed secondary to TPE. All 3 dogs were concurrently treated with either immunosuppressive agents, anticholinesterase drugs, or both.

NEW OR UNIQUE INFORMATION PROVIDED

The use of TPE in dogs with MG appears to be well tolerated and safe. It may be a reasonable adjunct therapy to acetylcholinesterase drugs in cases that are not responding to medical management alone. Therapeutic plasma exchange might also be considered preoperatively to prevent postoperative complications in dogs with severe MG, although further studies should be performed.

Classification of myasthenia gravis and congenital myasthenic syndromes in dogs and cats

Myasthenia, a syndrome of impaired neuromuscular transmission, occurs as either an acquired or congenital condition. Myasthenia gravis (MG) is an acquired autoimmune disorder with autoantibodies against the neuromuscular junction (NMJ) of skeletal muscle whereas congenital myasthenic syndromes (CMSs) are a clinically heterogeneous group of genetic disorders affecting the NMJ with a young age of onset. Both conditions are diseases for which recognition is important with regard to treatment and outcome. We review the published literature on MG and CMSs in dogs and cats, and by comparison with published classification used in humans, propose a classification system for MG and CMSs in dogs and cats. Myasthenia gravis is first classified based on focal, generalized, or acute fulminating presentation. It then is subclassified according to the autoimmune disease mechanism or seronegativity. Autoimmune disease mechanism relates to the presence or absence of a thymoma, or administration of thiourylene medication in cats. Congenital myasthenic syndromes are classified according to the affected NMJ component, the mechanism of the defect of neuromuscular transmission, the affected protein, and ultimately the mutated gene responsible. In proposing this categorization of MG and CMSs, we hope to aid recognition of the disease groups for both conditions, as well as guide treatment, refine prognosis, and provide a framework for additional studies of these conditions.

Clinical and serologic remission of acquired myasthenia gravis in a domestic ferret (Mustela putorius furo)

CASE DESCRIPTION

A 4.5-year-old neutered male domestic ferret (Mustela putorius furo) was examined because of clinical signs compatible with neuromuscular disease.

CLINICAL FINDINGS

Results of electrophysiologic assessment, including measurement of compound muscle action potentials following repetitive nerve stimulation, and measurement of the anti-acetylcholine receptor antibody titer were consistent with a diagnosis of acquired myasthenia gravis.

TREATMENT AND OUTCOME

Medical treatment with pyridostigmine and prednisolone was instituted. The first signs of clinical improvement were observed 2 months later, followed by a slow but steady improvement over the next months. Anti-acetylcholine receptor antibody titer was measured 10 months after initiation of treatment and was markedly decreased, compared with the initial titer. Pyridostigmine and prednisolone dosages were tapered over the following 4 months without any evidence of recurrence of clinical signs. Thirty months after initial examination, the ferret was clinically normal and not receiving any treatment. A follow-up anti-acetylcholine receptor antibody titer was similar to previously published values for healthy ferrets.

CLINICAL RELEVANCE

Findings indicated that clinical and serologic remission can be achieved in ferrets with myasthenia gravis. However, owner willingness to provide extensive supportive care was vital to the outcome for this patient, as was the owner's decision to not euthanize the ferret despite an initial lack of response to treatment.

The Dog Model in the Spotlight: Legacy of a Trustful Cooperation

Dogs have long been used as a biomedical model system and in particular as a preclinical proof of concept for innovative therapies before translation to humans. A recent example of the utility of this animal model is the promising myotubularin gene delivery in boys affected by X-linked centronuclear myopathy after successful systemic, long-term efficient gene therapy in Labrador retrievers. Mostly, this is due to unique features that make dogs an optimal system. The continuous emergence of spontaneous inherited disorders enables the identification of reliable complementary molecular models for human neuromuscular disorders (NMDs). Dogs’ characteristics including size, lifespan and unprecedented medical care level allow a comprehensive longitudinal description of diseases. Moreover, the highly similar pathogenic mechanisms with human patients yield to translational robustness. Finally, interindividual phenotypic heterogeneity between dogs helps identifying modifiers and anticipates precision medicine issues.

This review article summarizes the present list of molecularly characterized dog models for NMDs and provides an exhaustive list of the clinical and paraclinical assays that have been developed. This toolbox offers scientists a sensitive and reliable system to thoroughly evaluate neuromuscular function, as well as efficiency and safety of innovative therapies targeting these NMDs. This review also contextualizes the model by highlighting its unique genetic value, shaped by the long-term coevolution of humans and domesticated dogs. Because the dog is one of the most protected research animal models, there is considerable opposition to include it in preclinical projects, posing a threat to the use of this model. We thus discuss ethical issues, emphasizing that unlike many other models, the dog also benefits from its contribution to comparative biomedical research with a drastic reduction in the prevalence of morbid alleles in the breeding stock and an improvement in medical care.

Bite Forces and Their Measurement in Dogs and Cats

Bite force is generated by the interaction of the masticatory muscles, the mandibles and maxillae, the temporomandibular joints (TMJs), and the teeth. Several methods to measure bite forces in dogs and cats have been described. Direct in vivo measurement of a bite in dogs has been done; however, bite forces were highly variable due to animal volition, situation, or specific measurement technique. Bite force has been measured in vivo from anesthetized dogs by electrical stimulation of jaw adductor muscles, but this may not be reflective of volitional bite force during natural activity. In vitro bite forces have been estimated by calculation of the force produced using mechanical equations representing the jaw adductor muscles and of the mandible and skull structure Bite force can be estimated in silico using finite element analysis (FEA) of the computed model of the anatomical structures. FEA can estimate bite force in extinct species; however, estimates may be lower than the measurements in live animals and would have to be validated specifically in domestic dogs and cats to be reliable. The main factors affecting the bite forces in dogs and cats are body weight and the skull's morphology and size. Other factors such as oral pain, TMJ disorders, masticatory muscle atrophy, and malocclusion may also affect bite force. Knowledge of bite forces in dogs and cats is essential for various clinical and research fields such as the development of implants, materials, and surgical techniques as well as for forensic medicine. This paper is a summary of current knowledge of bite forces in dogs and cats, including the effect of measurement methods and of other factors.

Immunohistochemical analysis of canine and feline muscle disorders using formalin-fixed, paraffin-embedded tissues

Histochemical techniques used in examination of muscle biopsies typically require frozen sections. Given that most of the specimens submitted to a veterinary laboratory for diagnosis are formalin-fixed, the choice of staining methods is limited. We aimed to further advance the diagnostic capabilities of pathologists presented with formalin-fixed muscle samples and to describe the differences in immunohistopathologic findings between neurogenic and myogenic muscle disorders. Based on hematoxylin and eosin staining, we defined in dogs the histologic lesions in 4 neurogenic disorders (degenerative myelopathy and polyneuropathy) and 2 myogenic disorders (dystrophin-deficient muscular dystrophy). In cats, we defined the lesions in 2 neurogenic disorders (lymphoma of nerve roots and spinal cords) and 1 myogenic disorder (laminin α2-deficient muscular dystrophy). Immunohistochemistry for slow and fast myosins revealed angular and group atrophy of type 1 and type 2 fibers in dogs and cats, and fiber type grouping in dogs. These immunohistopathologic findings were specific to neurogenic muscle disorders. Immunohistochemistry for nestin and myogenin revealed nestin-positive fibers and myogenin-positive nuclei in dogs and cats. They were not specific, but these fibers in myogenic disorders can be interpreted as regenerating fibers. The immunohistochemical method described herein appears to be useful for discriminating neurogenic and myogenic disorders in formalin-fixed, paraffin-embedded muscle tissue of dogs and cats.

Temporal deterioration of neurological symptoms and increase of serum acetylcholine receptor antibody levels after thymectomy: a case report of a cat with myasthenia gravis

Neurological signs and serum acetylcholine receptor antibody (AChR-Ab) levels before and after thymectomy were monitored in a 6-year-old male cat with acquired Myasthenia Gravis (MG) as a paraneoplastic syndrome of thymoma. Soon after surgery, the neurological symptoms relapsed, and the cholinesterase inhibitor was administered to control them. The AChR-Ab levels increased postoperatively until 90 days after surgery. This is the first report on long term measurements of serum AChR-Ab levels in a cat with MG. Although thymectomy is valuable for the removal of thymoma, it may not resolve MG symptoms, neurological signs and serum AChR-Ab levels, without medication early after surgery. Also, this case report indicates that the AChR-Ab level might be a guide to detect a deterioration of MG symptoms.

Use of Lactate in Small Animal Clinical Practice

Lactate is a product of anaerobic metabolism. Lactate concentration in blood is used clinically as an indicator of tissue hypoperfusion and hypoxia to determine disease severity, assess response to therapy, and predict outcome. This article reviews lactate physiology, sample collection and processing, and interpretation of lactate concentration in clinical practice.

Congenital and inherited neurologic diseases in dogs and cats: Legislation and its effect on purchase in Italy

Many of the congenital neurologic diseases can result in incapacity or death of the animal. Some of them, such as idiopathic epilepsy and hydrocephalus, exhibit breed or familial predisposition and a genetic basis was proved or suggested. Some diseases can be presumptively diagnosed after a detailed signalment (breed predisposition), history (e.g. family history because many of these defects have familial tendencies), and through physical exam; other diagnostic methods (radiography, computed tomography, magnetic resonance, electrophysiologic tests, etc.) can provide supportive evidence for the congenital defect and help to confirm the diagnosis. Some cases can lead to civil law-suits when the lesions are congenital, but not easily recognizable, or when the lesions are hereditary but tend to became manifest only after some time (more than 12 months after the date of purchase, e.g., after the vice-free guarantee period has expired). Moreover, quite frequently an early diagnosis is not made because there are delays in consulting the veterinarian or the general practitioner veterinarian does not perceive subtle signs. This study was designed to focus on the medico-legal aspects concerning the buying and selling in Italy of dogs and cats affected by congenital and hereditary neurologic diseases that could constitute vice in these animals. While adequate provisions to regulate in detail the various aspects of pet sale have still to be drawn up by legislators, it may be helpful to involve breeders, by obliging them by contract to extend guarantees in the case of hereditary lesions, including neurologic diseases.

Risk Factors and Outcomes in Cats with Acquired Myasthenia Gravis (2001-2012)

Background

Acquired myasthenia gravis (MG) in cats most commonly causes generalized weakness without megaesophagus and is more often associated with a cranial mediastinal mass, compared to dogs.

Hypothesis/Objectives

To extend the clinical findings described in the report of 2000 on MG in cats (J Am Vet Med Assoc 215:55–57).

Animals

Two hundred and thirty‐five cats with MG.

Methods

Retrospective case study to evaluate the long‐term outcome and incidence of spontaneous remission in myasthenic cats. Information including signalment, clinical presentation, presence of and type of cranial mediastinal mass, treatment including surgical versus medical, survival time, and outcome including spontaneous remissions was collected and analyzed in cats diagnosed at the Comparative Neuromuscular Laboratory, University of California San Diego by detection of acetylcholine receptor antibody titers >0.3 nmol/L by immunoprecipitation radioimmunosassay.

Results

Acquired MG in cats is associated with a euthanasia rate of 58%. Abyssinian and Somali cats had an increased incidence of MG compared to mixed breed cats or cats of other breeds. A cranial mediastinal mass, most commonly thymoma, was observed in 52% of the cats, which is higher than in the previous report. Spontaneous remission is not a characteristic of MG in cats.

Conclusions and clinical importance

Myasthenia gravis in cats is a chronic disease associated with a high incidence of a cranial mediastinal mass. Spontaneous remission is not common and clinicians should warn owners of the necessity for long‐term treatment. The clinical outcome with a cranial mediastinal mass did not differ between surgical or medical treatment.

Dynamic exophthalmos and lateral strabismus in a dog caused by masticatory muscle myositis

CASE DESCRIPTION

A 5.5-year-old neutered male mixed-breed dog was presented for evaluation of a 5-month history of deviation of the right globe upon opening the mouth and a 1-month history of conjunctivitis in the same eye. Clinical findings, diagnostic imaging results, treatment and follow-up are described.

CLINICAL FINDINGS

When the mouth was opened, the right globe deviated rostrally and laterally. There was no pain or resistance to opening the mouth, or resistance to retropulsion of the globe. No other abnormalities were observed. Computed tomography was performed, revealing a contrast-enhancing region associated with the right masseter muscle impinging into the right orbit; this was more pronounced with the mouth open. Cytology revealed a small number of mildly to moderately atypical mesenchymal cells. Histopathology was consistent with polyphasic myositis, with a predominance of lymphocytes and plasma cells. No infectious agents were identified. Serum antibody titers for Toxoplasma gondii and Neospora caninum were negative. Serum titers for 2 M antibody were positive at 1:500, consistent with a diagnosis of masticatory muscle myositis.

TREATMENT AND OUTCOME

Therapy with prednisone was initiated. During a follow-up period of 5 months, there was no recurrence of clinical signs, and the dose of prednisone was reduced by 25%.

CLINICAL SIGNIFICANCE

To the authors' knowledge, this is the first reported case of masticatory muscle myositis causing dynamic exophthalmos and strabismus in a dog.

Principles and application of range of motion and stretching in companion animals

Optimal function after injury, surgery, or in patients with chronic conditions requires adequate motion in joints, muscles, tendon, fascia, and skin. Range of motion and stretching exercises are commonly used in companion animal rehabilitation programs to maintain or improve motion of musculoskeletal tissues. Range of motion exercises and stretching prevent adhesions from forming, help scar tissue remodeling, may improve muscle tone, and prevent future injury from occurring. Stretching is used to avoid loss of motion or to regain lost joint motion. Stretching is done manually, using external coaptation, or using therapeutic exercises. Careful documentation of range of motion is necessary.

Myopathy associated with congenital fibre type disproportion in a young dog

A 4-month-old, female collie-cross dog was presented for evaluation of slowly progressive weakness, exercise intolerance and muscle atrophy. Neurological examination and electrodiagnostic testing were consistent with a generalized myopathy or, less likely, an axonal polyneuropathy. Muscle biopsy samples revealed marked variability in myofibre size with scattered or clustered atrophic or hypotrophic type 1 fibres. Type 1 fibres were 65% smaller than type 2A fibres and the percentage of type 1 fibres exceeded reference values for both limb muscles examined. On the basis of the clinical evaluation, pathological changes and the absence of another defined congenital or acquired myopathy, a diagnosis of a myopathy associated with congenital fibre type disproportion was made. Three months later the animal was humanely euthanized because of worsening clinical signs.

Neuromuscular Disorders in the Cat: Clinical Approach to Weakness

Practical relevance Weakness is a relatively common clinical presentation in feline medicine and can be caused by primary neuromuscular disease or by diseases of other body systems affecting the neuromuscular system secondarily. Successful work-up relies on a thorough clinical and neurological examination, and logical problem solving, based on an understanding of the underlying neuroanatomical and pathophysiological mechanisms.

Clinical challenges Feline neuromuscular diseases can be a diagnostic challenge. On initial inspection, the presenting signs can mimic disorders of other body systems, particularly cardiovascular, pulmonary and orthopaedic disease, or may be confused with systemic illnesses. Additionally, because many different pathologies of the feline neuromuscular system converge to a similar clinical phenotype, further diagnostic steps such as electrodiagnostics, cerebrospinal fluid analysis, and muscle and nerve biopsies must be considered even after neuromuscular dysfunction has been identified.

Audience This review provides a framework for the clinical approach to the weak cat and gives a practical summary of neuromuscular diseases for the general practitioner and specialist alike.

Evidence base Many diseases affecting the feline neuromuscular system have been well described in the veterinary literature, mostly based on retrospective case reports and series. The evidence base for the treatment of feline neuromuscular diseases remains very limited.