Ventroflexion of the neck in cats is usually accompanied by generalised neuromuscular weakness so other locomotor signs may be present. Diagnosis is made on clinical signs and various laboratory tests, but sometimes trial and error testing with preparations (eg thiamine) is needed to determine the cause.
Ventroflexion of the neck is typically found in the following conditions (which are listed alphabetically):
Ammonium chloride toxicity
- Seen occasionally
- When ammonium chloride is used as a urine acidifier in the management of urolithiasis, the acidosis increases potassium loss through the kidneys and the resulting hypokalaemia causes muscle weakness and neck ventroflexion
Hereditary neck ventroflexion
- Rare
- An inherited defect has been described in Burmese cats (in the UK and Australia) which causes episodic stress-induced muscle weakness and neck ventroflexion
- The cause is not fully understood; may be transient hypokalaemia, or thiamine deficiency may be involved
- Affected cats should not be bred from
- Young Devon Rex cats (in the UK) have also been recognised with ventroflexion of the neck, which may be due to congenital muscular dystrophy
Hypernatraemia
- Rare
- This is seen in hypernatraemic cats which are hypodipsic
- Signs are transient and thought to be due to low intracellular potassium
- Creatine phosphokinase (CPK) is increased
Hyperthyroidism
- Uncommon
- A small percentage (less than 20 percent) of hyperthyroid cats will have muscle weakness and 1 to 3 percent will have ventroflexion of the neck
- The cause may be thyrotoxicosis or secondary due to inappetance and thiamine deficiency
Hypocalcaemia
- Rare
- Hypocalcaemia sometimes causes neck ventroflexion; other muscular signs include fasciculations, spasms, tetany and seizures
Hypokalaemia
- A common cause of neck ventroflexion and generalised muscle weakness
- Thirty percent of cats with chronic renal disease are hypokalaemic but only a few show neck ventroflexion
- There is usually a high CPK as well as low serum potassium
- Acidosis is an important factor in the development of hypokalaemia, and loop diuretics encourage potassium loss; azotaemia is also present
- Potassium supplementation should be given as soon as the diagnosis is confirmed (as the gluconate or chloride) Doses of 5 to 10 mEq divided twice daily orally to cats with less than 3 mEq/l serum potassium
- Improvement seen a over one-to-three-day period
- Feed a ration containing at least 0.6 percent potassium
- Treat underlying disease – use only potassium-sparing diuretics if necessary
Idiopathic polymyositis
- Uncommon
- Causes generalised muscle weakness, a stiff gait, muscle pain and ventroflexion of the neck
- Normal serum potassium, increased CPK, myofiber necrosis and lymphocytic infiltration is seen on histopathological examination of muscle biopsies
- Cause is unknown – may be immune-mediated
Myasthenia gravis
- Uncommon
- Both congenital and acquired myasthenia gravis occurs in cats
- Neck ventroflexion is the only clinical sign in 50 percent of these cases
- Other signs include: generalised weakness, abnormal gait, lagophthalmos. Occasional signs are muscle tremors, regurgitation of food and change in the voice
- Serum chemistry results are usually normal
- Improvement in signs is obtained by the administration of an ultra-short-acting acetylcholinesterase inhibitor (eg edrophonium chloride (0.5 to 1.0 mg/kg), or neostigmine (100 micrograms/kg). Care is needed with this test in case respiratory arrest is precipitated
- Anticholinesterase antibodies (AChR antibodies) will be present in cats with acquired myasthenia gravis, but not in cats with congenital myasthenia
- Muscle action potentials decrease in magnitude during repeated stimulation tests – but this is corrected by the administration of edrophonium
- Long term treatment is provided by pyridostigmine bromide – a long-acting acetylcholinesterase inhibitor – dose 2mg/kg by mouth every 8 to 12 hours
Organophosphate poisoning
- Cats are particularly susceptible to develop organophosphate toxicity (eg to insecticides) and the effects can be subacute or chronic following multiple exposures. The result is acetylcholinesterase inhibition producing a myasthenia-type disorder with muscle weakness and ventroflexion of the neck
- Other signs include dilated pupils and muscle tremors
- If edrophonium is given to these cases their condition may worsen, and edrophonium does not eliminate the decreased action potential in repeatedly stimulated muscle
- Atropine will not block the nicotinic receptor overstimulation that causes the neck ventroflexion, but diphenhydramine does (4mg/kg by mouth every eight hours). This drug must be used with caution in cats – side effects include CNS excitation, sedation and anorexia
Polyneuropathy (idiopathic or secondary)
- Rare
- Secondary polyneuropathy associated with diabetes mellitus is the most often recorded – but this form of polyneuropathy causes poor posture and slow limb reflexes not ventroflexion of the neck
- Idiopathic polyneuropathy does lead to ventroflexion of the neck
Portosystemic encephalopathy
- Uncommon sign seen with this disease
- Other signs include depression, stupor, pacing, circling, ataxia, blindness, collapse, head pressing, personality changes, seizures, hyperactivity, ventroflexion of the neck, muscle tremors, deafness and coma
- Diagnosis based on clinical signs, elevated liver enzymes on blood chemistry and high fasting blood ammonia and abnormal serum bile acid concentrations
Thiamine deficiency
- Uncommon
- Thiamine (Vitamin B1) deficiency is uncommon as commercially prepared complete cat foods contain adequate concentrations; however, many cases of ventroflexion of the neck in cats are thiamine-responsive
- Thiamine is a co-enzyme needed for energy production and deficiency causes polyneuropathy and polymyopathy
- Other signs include dilated pupils with a poor light reflex
- Thiamine is given at 25 to 50mg daily by intramuscular injection for two to three days
- Head carriage returns to normal in one to two days
- Creatine kinase (CPK) concentrations may increase after thiamine treatment
This information is provided by Provet for educational purposes only.
You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.
