Table 3: Common differential diagnosis for CM-P and SM and unrelated comorbidities common in CKCS
ConditionClinical signsNotes
Other neurological signs
Idiopathic epilepsySeizures, normal interictal neurological examinationNo link between CM/SM and epilepsy has been proved. Considered separate diseases for management purposes
Paroxysmal dyskinesia (epileptoid cramping syndrome/Spike’s disease)Episodes of abnormal movement that are self-limiting with long periods of normality between episodes. Abnormal movements may include tremor, alternate limb lifting/flexion and weaving head movements with variable gastrointestinal signs. Animal remains conscious and able to respond to owner (eg, may try to walk to owner)Possible connection to gastrointestinal dysfunction and gluten sensitivity. Episodes may reduce with a hypoallergenic or gluten free diet
Fly catching disorderBehaviour where the dog acts as if watching/catching a fly (although ignores actual flies). Some may also behave as if their ears or feet are irritated and some can also tail chase. May be more likely with certain light intensities and emotional statesPossible connection to gastrointestinal dysfunction. Episodes may reduce with a hypoallergenic or low protein diet. Neurochemical imbalance has been suggested as some dogs respond to anti-epilepsy drugs or selective serotonin re-uptake inhibitors
MyoclonusBrief jerking of the head, often with buckling of a thoracic limb when the dog is standing or sittingOlder CKCS (over five years old). Initially relatively benign but can be progressive over years and the myoclonic jerks can cause the dog to fall or stumble
Episodic falling (paroxysmal exercise-induced dyskinesia)Falling episodes induced by physical activity, stress and excitement, and manifest with hypertonicity of the limbs resulting in inability to move or even complete collapse. In contrast to epileptic seizures, consciousness is unaffectedMovement disorder associated with BCAN (brevican) mutation. Typically manifests between the age of four months and four years. A genetic test is available
Idiopathic facial paresisInability to close the eye or move the lips, ears or other facial muscles. Facial sensation (trigeminal nerve) is normalMay be bilateral (not necessarily simultaneously) in CKCS, or associated with vestibular signs
Other causes of head tilt
Idiopathic vestibular diseaseAcute onset vestibular signs (head tilt, nystagmus, positional strabismus, asymmetrical ataxia) with no proprioceptive deficits or weaknessIn CKCS idiopathic vestibular disease has two variations: one in geriatric dogs and one in middle-aged dogs often in conjunction with idiopathic facial paresis
Rostral cerebellar artery infarctionAcute-onset paradoxical vestibular signs with other signs suggesting a cerebellar location (menace response deficit, intention tremor, decerebellate posture)Often improves with supportive care
Other causes of spinal pain or myelopathy (proprioceptive deficits and paresis)
Atlantoaxial subluxationMyelopathy localising to the cranial cervical spinal cord (tetraparesis, increased muscle tone, proprioceptive deficits and possible respiratory compromise)May be seen in association with CM-P and SM, especially in miniature breeds such as Chihuahuas and Yorkshire terriers
IVDD – cervicalNeck pain and variable limb postural deficits. May be associated with neck muscle myoclonus (C3 nerve root compression/irritation) or lameness (C5-C8 nerve root compression/irritation)In contrast to CM/SM, IVDD typically occurs in older dogs (two years of age or older) and spinal pain is typically acute onset and focal
IVDD – thoracolumbarAcute-onset focal pain in T11-L4 region with variable myelopathy (paraparesis and proprioceptive deficits)
IVDD – lumbosacralRefusal/hesitation/difficulty in jumping or climbing the stairs. Focal pain in lumbosacral region. Unilateral or bilateral pelvic limb lameness. Hyperaesthesia in the distribution of the L7 nerve root
Meningoencephalomyelitis of unknown originSpinal pain with variable neurological signs relating to immune-mediated inflammation of the brain or spinal cordInflammatory disease will also result in a high intrathecal signal on T2 weighted images (see Fig 4)
Degenerative myelopathy associated with gain of function SOD-1 mutationPelvic limb proprioceptive deficits and paraparesis (T3-L3 localisation), progressing over months to paraplegia with faecal and urinary incontinence, and over years to tetraplegia. Non-painfulEven with wide SM, significant pelvic limb weakness and proprioceptive deficits is unusual and other differentials should be considered. A genetic test for the SOD-1 mutation is available
Other causes of head and ear rubbing or scratching
Otitis media with effusion (OME; also known as primary secretary otitis media)Sequel of brachycephalic conformation and poor drainage of the middle ear. May cause hearing loss or ear discomfortOME is a possible differential for ear pain or rubbing (Guerin and others 2015); however, Rusbridge and others (2019) did not find OME presence significantly associated with head/ear rubbing or scratching
Allergic skin diseaseGeneralised pruritus, especially of the feet and abdomenCM-P and SM are not associated with pruritus of the ventral abdomen, feet or tail head
Periodontal diseaseOral pain with inflammation of the gingiva and deterioration of the bone and soft tissue structures supporting the teethHigher prevalence in small breeds and significant association with cardiac disease (Pereira dos Santos and others 2019)
Other causes of sleep disruption, exercise intolerance or lethargy
Brachycephalic obstructive airway diseaseExercise, heat intolerance, sleep disordered breathing or sleep apnoeaImportant differential for sleep disruption. Consider if the dog is waking up spluttering or coughing
Degenerative mitral valve diseaseLeft apical systolic murmur, exercise intolerance, coughing, respiratory effort, nocturnal dyspnoea, pulmonary oedemaImportant differential for exercise intolerance
Chronic pancreatitisRecurrent anorexia, mild bouts of colitis-like faeces, occasional vomiting, increased borborygmi, mild abdominal painDifferential for signs of lethargy and behavioural changes suggesting pain
Gastro-oesophageal reflux diseaseClassic signs like regurgitation not always present/obvious. Discomfort or pain may manifest as repetitive tongue licking or restlessnessDifferential for behavioural changes suggesting pain
  • CKCS Cavalier King Charles spaniel, CM-P Chiari-like malformation-associated pain, IVDD Intervertebral disc disease, SM Syringomyelia, SOD1 Superoxide dismutase 1