“Head-down syndrome” in a rabbit

Possible causes

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Kathleen Bourdelais Midnight (black rabbit) is happily living with 2 other rabbits. The days before the inability to hold its head high, Midnight was healthy, with an upright head, no appearance of the third eyelid.

Acute onset of “head-down syndrome”, also referred to floppy head syndrome or dropped head syndrome, has been observed in rabbits. The head is tilted forward and rabbits seem unable to lift it. The forward flexion is caused by weakness or contraction of the extensor muscles in the neck, which leads to the inability to hold the head upright and against the force of gravity. There is no tilting to the side. It may be accompanied by reluctance to move, decrease of appetite and pain.

Reminder: rabbits feel very insecure on smooth, slippery surfaces or floors. Please-remember to give your rabbit a rug or towel made of natural materials (especially rabbits who like to chew) so that the rabbit's feet will not slip or cause any injuries through an inadvertent accident.
Kathleen Bourdelais Rabbit suffering from “head-down syndrome”, the inability to lift the head, reluctance to move and appearance of the third eyelid. On the first day, it also suffered stasis-like signs. Appetite resumed rapidly on the 2^nd day of this syndrome.

It is important to differentiate between muscle weakness in the neck region, and excessive contraction of the muscles. Typically, necks weakness relates to one of these categories: motor neuron disease, auto-immune muscle disorder (myasthenia gravis-like), inflammatory muscle disease (polymyositis-like) or idiopathic, while contracted neck muscles relate to torticolis or neurotoxins. Since the flexion of the head is forward and not to the side, it is unrelated to an active infection by Encephalitozoon cuniculi or middle/inner ear infection.

In spite of a complete physical examination and diagnostic tests such as blood tests, radiography, and the history of the rabbits, the etiology of this disorder remains uncertain. Veterinarian were puzzled by this health disorder. What could it be ?

A few years ago, rabbit presented the exact same clinical features and blood chemistry results and vets were amazed about his condition too: Twilight.

A closer analysis of the blood chemistry panel of Midnight and Twilight indicates high liver values (AST, ALT, Alk Phosphatase) and a low level phosphorus (hypophosphatemia). Hypophosphatemia has typically been associated with fulminant hepatic failure as well as increased metabolism of phosphorus during hepatic function recovery and hepatocyte regeneration. A working hypothesis is that these rabbit may have suffered hepatic encephalopathy as a consequence of fulminant liver failure and a raised level of blood ammonia.

Blood chemistry panel of Midnight. It shows close parallels with that of another rabbit, Twilight, who suffered a similar disease a few years ago. This could be indicative of hepatic encephalopathy.

(click on the picture to see the full results of the blood test)

Affected rabbits were given antibiotics, fenbendazole and metacam. Treatment consists of supportive care, antibiotics, control of pain, force-feeding when necessary. Most animals recover between 7 to 14 days. If needed, subcutaneous fluids and feeding with a syringe should be started. Prognosis is guarded to good. All affected rabbit recovered within a week.

The following table’s list causes related to difficulties to hold the head high as observed in other herbivorous animals, horses, cattle, sheep and goats. Further causes cannot be excluded.

Neurotoxic causes	Numerous members of Clostridium sp. bacteria release neurotoxins in the blood of infected animals. They can lead to muscle cramps. Botulism, caused by C. botulinum has been observed in herbivore farm animals. It is caused by rotten hay. Poor function of cranial nerves can lead to the dropping of the head. It can be accompanied by weakness in the limbs (flaccid quadriparesis) and decreased reflexes.
	Tick paralysis. Some tick species are known to release toxins in the saliva, when biting their host: some species of Dermacentor sp. in the US, Ixodes holocyclus in Australia. Generally local paresis (paraparesis) develops into flaccid quadriparesis or quadriplegia, accompanied by weak or absent spinal cord reflexes.
	Toxins released by black widow spiders. Muscle weakness can lead to ptosis of the head. It may be accompanied by swollen eyelids, drooling, pain, and/or difficult breathing.

Bacterial causes	Pyogranulomatous meningo-encephalomyelitis can lead to kyphosis, inability to raise the head and neck rigidity. The animal presents an inability to coordinate movement and limbs and a reluctance to move. When not treated, atrophy of cervical muscles can occur.
	Infection in the spine

Liver disease

Hepatic encephalopathy

Spine abnormalities	Bent spine syndrome
	Ankylosing spondylitis
	Vertebral fracture

Neuropathic or neuromuscular disorders	Myasthenia gravis can cause weakness of the neck muscles. It is generally accompanied by weakness of front limbs, difficulties to swallow food
	Motor neuron disorders
	Reversible demyelinating (poly)neuropathy

Myopathic troubles	Myositis
	Muscle Dystrophy
	Congenital myopathy

Hormonal causes

Hypothyroidism

Mechanical trouble	Trauma
	Presence of a brain or spine tumor

Medication	Certain anti-nausea drugs
	Phenothiazine

Depending on the cause, the inability to hold the head upright is reversible or irreversible. Recovery may be fast, within a week, or take weeks to months. Prognosis is guarded to good. Treatment consists of supportive care, antibiotics, fluid management, control of pain, force-feeding when necessary.

Many thanks to Kathleen Bourdelais, Suzanne Trayhan and Bonnie Salt for sharing the information about Midnight

and for the permission to use the pictures and videos.

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