Reversible positioning head tilt observed in 14 cats with hypokalaemic myopathy

Abstract

Case series summary Positioning head tilt (PHT) is a dynamic neurological sign in which the head tilts to the opposite side to which it is moving. This sign is triggered in response to head movement and is thought to be due to the lack of inhibition of vestibular nuclei by the cerebellar nodulus and uvula (NU). The occurrence of PHT in animals has been suggested to be an indicator of NU dysfunction. Here, we describe the acute onset of PHT in 14 cats. All the cats were diagnosed with hypokalaemic myopathy caused by a range of pathologies. The PHT resolved along with other signs related to myopathy, such as cervical flexion and generalised weakness, after electrolyte correction in all cats. Relevance and novel information Hypokalaemic myopathy was the likely cause of PHT in the present feline cases.

Positioning head tilt observed in two cats with myasthenia gravis

“…A mechanism for PHT seen in cats with hypokalaemic myopathy has been suggested. 7 Hypokalaemia causes dysfunction of muscle spindles in the cervical muscles. Because intrafusal fibres consist of skeletal muscle fibres and are affected by hypokalaemia, proprioception input from the muscles is lost, which prevents the nodules and uvula from producing inhibitory output against reflexive head tilting toward the opposite side of the head movement.…”

“…Because intrafusal fibres consist of skeletal muscle fibres and are affected by hypokalaemia, proprioception input from the muscles is lost, which prevents the nodules and uvula from producing inhibitory output against reflexive head tilting toward the opposite side of the head movement. More specific observations are warranted to verify whether PHT is also observed in other muscle diseases, such as muscular dystrophy and MG, 7 because the proprioceptive system deficit owing to muscle spindle dysfunction is also observed in human patients with muscular dystrophy. 8 Impaired proprioception, which can be associated with altered muscle spindle morphology in some cases, has been documented to be a secondary effect of human MG. 9 Although the pathophysiology of PHT in cats is not fully understood, its role as a mechanism for PHT in cats with MG may be similar to its role in cats with hypokalaemic myopathy, supporting our hypothesis that muscle spindle dysfunction causes PHT.…”

“…Behavioural posturing of the head to increase the visual field of view can also cause head tilting in cats with weakness, the same as PHT in feline hypokalaemic myopathy. 7 …”

“… 1 , 2 PHT has been reported in dogs with the cerebellar nodulus and uvula (NU) hypoplasia, 1 in dogs with five different types of lysosomal storage disease, 3 in one case of a dog with gliomatosis cerebri affecting NU 4 – 6 and in cats with hypokalaemic myopathy. 7 The mechanism for PHT can be explained by the following hypothesis: in order to maintain equilibrium of the head while moving, the vestibular nuclei contract the oblique and rectus capitis muscles bilaterally through the vestibulospinal tract based on information provided by movement from the vestibular apparatus. 1 , 2 The NU regulates these muscles with inhibitory outputs to achieve head equilibrium.…”

“… 7 Since head equilibrium is maintained by this mechanism, PHT is caused by dysfunction of either the NU 1 , 3 – 6 or the muscle spindle of the obliquus and rectus capitis muscles. 7 …”