Richard A. LeCouteur, BVSc, PhD, DACVIM (Neurology), DECVN
Feline neuromuscular diseases may be classified according to their location as those involving peripheral nerves and/or nerve roots, those involving the neuromuscular junction, and those that involve muscle (1). Each of these neuromuscular diseases will produce lower motor neuron (LMN) disease, however significant variations in clinical signs may occur. Peripheral nerve and muscle diseases result in varying degrees of paresis, muscle atrophy, hyporeflexia, and hypotonia. Hyporeflexia, hypotonia, ataxia and proprioceptive positioning deficits are most characteristic of peripheral nerve disease. Some primary muscle disorders may be characterised by muscle hypertrophy rather than atrophy. Neuromuscular junction disorders ("junctionopathies") result in a variety of clinical signs that range from flaccid paralysis to exercise-induced weakness.
Cervical ventroflexion is a dramatic sign of generalised neuromuscular weakness in cats. The chin usually rests near the thoracic inlet, with the eyes positioned dorsally to maintain a straight-ahead gaze. Other common physical examination findings are a slight protrusion of the dorsal aspects of the scapulae when weight is placed on thoracic limbs, and a stiff thoracic limb gait. A crouched, wide-based stance is often seen in pelvic limbs.
Megaoesophagus rarely has been reported in cats, although a predisposition has been noted in Siamese and Siamese-related breeds. In most cats the cause of acquired megaoesophagus is unknown.
Feline Dysautonomia: A generalised disorder of autonomic ganglia. There is no age or breed predilection for this disease. The disorder is a neuronal disorder; however, clinical signs relate more to autonomic dysfunction, and are largely gastrointestinal in nature. The most common signs are depression, anorexia, constipation, dry external nares and oral mucosa, reduced tear production, regurgitation, protrusion of the membrana nictitans, mydriasis, and bradycardia.
Tetanus: The Clostridium tetani exotoxin interferes with release of neurotransmitters from inhibitory interneurons in the spinal cord. Local tetanus has been reported in cats.
Feline Motor Neuron Diseases: A group of disorders characterized by degeneration and loss of motor neurons.
Sphingomyelinase-deficiency polyneuropathy' hyperchylomicronemia-associated neuropathy, hyperoxaluric peripheral neuropathy, hypertrophic polyneuropathy, and Birman cat distal polyneuropathy are examples of inherited polyneuropathies.
Diabetic Polyneuropathy: A distal polyneuropathy has been reported in cats with uncontrolled or poorly controlled diabetes mellitus. Neurological abnormalities include a plantigrade stance, progressive paraparesis, muscle atrophy, and patellar hyporeflexia.
Ischemic Neuromyopathy: Occurs in cats with cardiomyopathy, subsequent to thrombosis of the caudal aorta or its principal branches.
Trauma: Brachial plexus avulsion produced by severe thoracic limb abduction with secondary stretching or tearing of nerve roots is a commonly occurring peripheral nerve injury of cats. Sacroiliac fracture/dislocation, sacral fracture, or caudal vertebral fracture/luxation may result in damage to the sixth and seventh lumbar and first 2 sacral nerve roots. Mononeuropathies of radial nerve and sciatic nerve occur in cats following mechanical blows, gunshot wounds, fractures, pressure and stretching.
Neoplasia: Feline malignant lymphoma may involve nerve roots or peripheral nerves. Other primary peripheral nerve neoplasms rarely are seen in cats.
Toxic Neuropathies: Drug-induced neuropathies are not well defined in cats.
Laryngeal Paralysis: Acute laryngeal paralysis may be diagnosed in cats with signs of upper airway obstruction, including dysphonia, absence of purring, and progressive inspiratory dyspnea.
Miscellaneous Peripheral Polyneuropathies: Single case reports exist of a variety of peripheral neuropathies in cats. These include: inflammatory polyneuropathy (a chronic relapsing polyradiculoneuritis) and an acute polyneuritis, an idiopathic chronic relapsing polyneuropathy responsive to immunosuppressive glucocorticoid therapy, and an acute brachial plexus neuropathy with a suspected relationship to a previous vaccination.
Myasthenia Gravis: Myasthenia gravis is a condition that results from either an inherited or an acquired reduction of acetylcholine receptors of neuromuscular junctions. The most consistent signs in cats include tremors, initial stiffness with progression to generalised weakness on exercise, cervical ventroflexion, dysphagia, dysphonia, ptyalism, facial weakness, and dyspnea. Overt megaesophagus or esophageal hypomotility are common.
Miscellaneous "Junctionopathies": Abnormalities in neuromuscular junction function also may result from tick paralysis, administration of certain drugs, selected toxins, or from envenomation. Botulism has not been reported as a clinical entity in cats, however, it may be produced experimentally in cats.
Muscular Dystrophy: Muscular dystrophy-like disorders of cats have been. Clinical signs may first be seen in cats at 5-6 months of age, and include generalised skeletal muscle hypertrophy, excessive salivation, reduced exercise tolerance, stiff gait and "bunny-hopping" when running, difficulty in jumping, adducted hocks, cervical rigidity, vomiting/regurgitation, and partial protrusion of the tongue.
Miscellaneous Inherited Myopathies: Myotonia congenita, nemaline myopathy, myositis ossificans, and glycogen storage diseases (or glycogenoses) have been reported in cats.
Infectious Polymyositis: Infectious myositis may occur in association with bacterial infection, migrating parasites, or protozoan disease.
Polymyositis: Polymyositis occurs sporadically in cats, occasionally in association with thymoma. Clinical signs are characterised by a persistent cervical ventroflexion, appendicular weakness, painful muscles, and exercise intolerance. Serum levels of creatine kinase and aldolase are elevated.
Potassium-depletion Polymyopathy: This acute feline polymyopathy, resulting from a severe total body potassium depletion, is usually secondary to a reduced potassium intake and increases in the fractional excretion of potassium in urine (due to renal dysfunction). Clinical signs include muscle weakness, cervical ventroflexion, stiff and stilted gait, and muscle pain. A similar syndrome with a suspected hereditary basis has been reported to occur in Burmese cats.
Miscellaneous Myopathies: There are a number of case reports of muscle-related diseases of cats (e.g., nutritional myopathy secondary to vitamin E deficiency, myositis secondary to Clostridium chauvoei and Clostridium septicum infections, fibrotic myopathy of the semitendinosus muscle, quadriceps contracture secondary to trauma, and hypernatraemic myopathy).
1. Dickinson PD, LeCouteur RA. Muscle and nerve biopsy. Veterinary Clinics of North America Small Animal Practice 2002; 32: 63-102.
2. Dickinson PD, LeCouteur RA. Feline Neuromuscular Disorders. Veterinary Clinics of North America Small Animal Practice 2004; 1307-1360.