Lesion localisation

Lesion localisation is the most important information in the clinical neurology. The easiest way to arrive to the neuroanatomical lesion localisation is with the help of several questions and answers:

1 question:

Is the patient having MONOPARESIS (just strictly one limb is affected)? 

If the answer to this question is "yes", than the most likely lesion localisation will be in the peripheral nervous system of the affected limb!

2 question:

Is the patient having weakness in all 4 limbs and has GENERALISED DECREASED SPINAL REFLEXES?               

If the answer to this question is "yes", than the most likely lesion localisation will be in the the peripheral nervous system: generalised or diffuse problem!

3 question:

Is the patient having CRANIAL NERVE ABNORMALITY? 

If the answer to this question is "yes", than the lesion localisation will be above the foramen magnum, intracranialy!

4 question:

Have the first three answers been "no"?

If the answer to this question is "yes", than the lesion will be located within the spinal cord!

EXPLANATION FOR THE LESION LOCALISATION

Monoparesis/monoplegia: weakness in one single front limb is always peripheral (usually nerves or nerve roots, seldom muscle(s)). The monoparesis in one hind  limb might be caused by spinal cord or peripheral lesion. Lesions in the peripheral nervous system of the affected limb are the most frequent. The spinal cord disease most frequently causing the monoparesis in the rear is the fibrocartilaginous embolism. 

Tetraparesis/tetraplegia with generalized decreased spinal reflexes is usully caused by a diffuse lesion in the peripheral nervous system (polyneuropathy, polymyopathy). These diseases are rather frequent and is important to distinguish them from the cervical lesions which will cause tetraparesis also. The detection of generalised decreased reflexes (reflexes decreased in all 4 limbs) is crucial as it is indicating that multiple nerves or muscles are affected.

Detection of cranial nerve abnormalities is indicating the presence of lesion above foramen magnum. It might be located in the brain or in the peripheral portion of the cranial nerve(s). The further differentiation between the forebrain, brainstem and cerebellar disease is performed according to the findings of the examination of the gait. If animal has normal gait the forebrain lesion is likely, if the patient is showing signs of paresis (hemi- or tetraparesis) the brainstem lesion has to be suspected and if the dog is having generalised ataxia with hypermetria the cerebellum will be the most likely lesion localisation. Head tilt clearly indicates that the lesion is in the vestibular system. Peripheral vestibular lesion is usually not causing deficits in proprioceptive positioning and the central vestibular lesion is usually causing delay in this postural reaction.

Paraparesis/paraplegia or weakness of both hind limbs is indicating that lesion is in the spinal cord caudally to Th3 (Th3-S3). Tetraparesis/tetraplegia or hemiparesis/hemiplegia with normal or exaggerated spinal reflexes  in the rear and normal cranial nerves indicates that lesion is in the cervical spinal cord (C1-Th2). Further differentiation between the C1-5 and C6-Th2 segments is based on the spinal reflex examination findings in the front limbs. If reflexes are normal lesion is in C1-5, if reflexes are decreased, lesion is in C6-Th2. Similarly the lesion is differentiated between the segments Th3-L3 and L4-S3: the reflexes in the rear are normal or exaggerated in Th3-L3 lesions and decreased in L4-S3 lesions.

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