False Localising Signs In Neurology.pptx

False localizing signs in neurology, cranial nerves, brain

1. FALSE LOCALISING SIGNS IN NEUROLOGY Indian Journal of Clinical Practice, Feb 2013: 553-559.

2. SPECIFIC LOCALIZING SIGNS Signs elicited during neurologic examination are thought to be SPECIFIC / FOCAL LOCALIZING SIGNS if their presence indicates a lesion at a specific area in the nervous system. The neurologist must decide whether the symptoms and signs could all arise from one focal lesion, or whether several anatomical sites must be involved. The Principle of Parsimony, or Occam’s Razor, requires that the clinician strives to hypothesize only one lesion. The differential diagnosis for a single focal lesion is significantly different from that for multiple lesions.

3. OCCAM’S RAZOR

4. FALSE LOCALIZING SIGNS In contrast, Clinical features caused by damage far from the primary site of abnormality are called False Localising Signs. Reflect dysfunction distant from the expected anatomical location of pathology Challenge the traditional clinico -anatomical correlation paradigm on which neurological examination is based. Falseness exists with the Interpretation of the findings.

5. HISTORY The term derives from the era before neuroimaging studies, when clinical examination was the major means of lesion localization. James Collier first described cerebellar tonsillar herniation in 1904 Subsequent scientists noted them to be more common in raised ICP.

6. PATHOGENESIS Presence suggests that intracranial shifts are marked. Indicating the presence of markedly raised ICP, or large space occupying lesions in the skull. The “ False”hood is in the interpretation.

7. PATHOGENESIS False localizing signs occur in two common contexts: As a consequence of raised ICP, which may be: Secondary to or symptomatic of intracranial pathology ( tumor , hematoma, abscess), or Primary, or Idiopathic (IIH), and Spinal Cord Lesions Course: acute (intracranial hemorrhage ), or chronic (IIH, tumor )

8. CORTICAL FUNCTIONS APHASIA Subcortical aphasia may result from lesions of: Basal ganglia, Anterolateral nuclei of the thalamus, and Peri -capsular white matter of the dominant hemisphere. Lesions of post limb of the int capsule ( ICp ) typically produces aphasia with: Rapid fluent speech with paraphasias and extended jargon, Poor comprehension, and impaired repetition. J Neuropsychiatry Clin Neurosci 27:2, Spring 2015

9. CORTICAL FUNCTIONS Lesions of the ant limb of int capsule ( ICa ) (and often the genu [ ICg ]) typically produces aphasia with: Grammatical but slow dysarthric speech, Impaired syntactic comprehension, and Impaired repetition for low-probability sentences Impaired articulatory agility, buccofacial apraxia. Concomitant neuropsychiatric disturbances (executive dysfunction, diminished motivation, emotional lability ) J Neuropsychiatry Clin Neurosci 27:2, Spring 2015

10. CORTICAL FUNCTIONS An atypical variant involving posterior shift of corticonuclear , corticospinal , and sensory fibers within the ICp would concurrently permit broader distribution of frontopontine , thalamofrontal , and thalamostriate pathways from the ICa into the ICg and the anterior portion of the ICp . Variant capsular anatomy of this nature offers a parsimonious explanation for this patient’s clinical presentation with poststroke subcortical aphasia and neurobehavioral disturbances without motor or sensory deficits. J Neuropsychiatry Clin Neurosci 27:2, Spring 2015

11. J Neuropsychiatry Clin Neurosci 27:2, Spring 2015

12. CRANIAL NERVES MECHANISM OF CRANIAL NERVE SIGNS: Extrinsic compression of the nerve on the tentorial margin or petrous temporal bone, M. C. Localising. Kinking or Stretching of the nerves in their intracranial course, over the clivus , just posterior to the clinoid , due to raised ICP, M. C. False Localising. Supratentorial pressure causing the brainstem to buckle as it descends because of caudal tethering of the neuraxis at the first dentate ligament (“dynamic axial brainstem distortion”)

13. CRANIAL NERVES There may be Hypo- or Hyper-function of a cranial nerve, Manifesting as negative or positive symptoms, resp. Negative symp - Sensory Neuropathy or motor weakness Positive symp - Neuralgia PATHOPHYSIOLOGY: Vascular compression of nerve root causes paroxysmal ephaptic transmission, Angulations and distortion of nerve root entry/exit zone due to mass effect produces focal neuropathy Adherence of arachnoid membrane to the nerve

14. CRANIAL NERVES PAPILLOEDEMA cannot be reliably used as an indication of elevated intracranial pressure because its leading cause in late life is ischemic optic neuropathy. HUTCHINSON’S PUPIL = Unilateral fixed dilated pupil Compression of III N. Ipsilateral to lesion  more common Contralateral to lesion  FL Brain Inj. 2009 July ; 23(7): 597–601.

15. CRANIAL NERVES DIVISIONAL III N PALSY In keeping with the topographic arrangement of the fascicles within the nerve, Focal : Ant Cavernous Sinus, or Sup Orbital Fissure False : with intrinsic brainstem disease (e.g. stroke), or with pathology in the subarachnoid space where the nerve rootlets emerge from the brainstem (e.g. malignant infiltration).

16. CRANIAL NERVES INTERNUCLEAR OPHTHALMOPLEGIA Focal: Demyelination in Medial Longitudinal Fasciculus False : Myasthenia gravis, Guillain – Barré syndrome, and Miller Fisher syndrome Dermatomyositis SDH  transtentorial herniation  brainstem compression Cerebellar masses,

17. CRANIAL NERVES TRIGEMINAL NERVE Hypofunction : Trigeminal Sensory Neuropathy, e.g. in IIH, unilateral > bilateral Hyperfunction : Trigeminal Neuralgia, e.g. with chronic calcified SDH causing rotational displacement of the pons . Contralat posterior fossa tumor  Trigeminal Hypofunction  Surgical removal of tumor  Trigeminal Neuralgia Neuralgia is a lesser degree of dysfunction than neuropathy.

18. CRANIAL NERVES SIXTH CRANIAL NERVE Sixth nerve palsy is the M.C. false-localizing sign of raised ICP. The deficit is remote from the site of the process producing intracranial hypertension, hence false localizing. Included in diagnostic criteria for IIH (Other C.N. is VII). In one series of 101 cases of IIH, 14 cases were noted, 11 unilateral and 3 bilateral.

19. CRANIAL NERVES SEVENTH CRANIAL NERVE LMN type of facial weakness is described in IIH, Sometimes B/L to produce facial diplegia . Hemifacial spasm – Contralateral posterior fossa lesions. EIGHTH CRANIAL NERVE Occasional Complication of IIH

20. CRANIAL NERVES Contralat Acoustic Neuroma  V, VI, VII nerve palsies Contralat Laterally placed posterior fossa meningioma  V, IX, X nerve palsies

21. KERNOHAN-WOLTMAN NOTCH PHENOMENON Supratentorial Lesion  Transtentorial Herniation of Temporal Lobe  Compression of Cerebral Peduncle against Tentorial Edge Focal : Ipsilateral CP  Contralateral Hemiparesis False : Contralateral CP  Ipsilateral Hemiparesis Assoc. Ipsilateral III N Palsy usually present. Mechanism: Downward pressure  compression of the contralateral incisura of the crus cerebri by the tentorial edge. Incisura of crus cerebri = Kernohan-Woltman Notch Imaging of Kernohan’s Notch now possible by MRI. Brain Inj. 2009 July ; 23(7): 597–601.

22. CERVICOMEDULLARY JUNCTION Aberrant Vertebral Artery  Ipsilateral Medullary Compression  Hemidiaphragmatic Paralysis Paresthesia in the hands, intrinsic hand muscle wasting, distal upper limb areflexia , with or without long tract signs (suggestive of a lower cervical myelopathy ) may occur with lesions at the foramen magnum or upper cervical cord (‘remote atrophy’).

23. SPINAL CORD Patients with cervical spondylosis Painful stiff neck and diffuse nonpulsatile headache that resolves in a few hours of waking. Lesion is most commonly at C5/6 and/or C6/7, and have corresponding focal signs reflecting root dysfunction. However, Wasting and weakness of the small muscles of the hands (esp. abduction of the little finger) is often present. This sign localizes to lower segmental levels but there may be no observable anatomical change at those levels and it is labeled as a false localizer. Compressive lower cervical or upper thoracic myelopathy may produce spastic paraplegia with a mid-thoracic sensory level (or ‘girdle sensation’). Lumbar spinal disease may be simulated by more rostral pathology. Urinary retention, leg weakness, and lumbar sensory findings may be the presenting features of high thoracic cord compression, with clinico -radiological discrepancy of as much as 11 segments.

24. SPINAL CORD Three principal mechanisms have been invoked: arterial, venous, and mechanical. Arterial hypothesis : tumour / disc compromises descending anterior spinal artery blood supply to lower cervical cord  focal ischemia. Midline ventral portion of cervical cord was markedly compressed in those with false localising sensory level, s/o ischemia in the watershed zone of the anterior spinal artery, affecting the medial portion of the laminations of the spinothalamic tract, as the causative mechanism for discrepancy Venous hypothesis : low pressure venous system is inherently more vulnerable to compression than arterial  tissue stasis and hypoxia  neurological dysfunction. Mechanical hypothesis : Extrinsic compression + anchoring of spinal cord by the dentate ligaments  Mechanical stress  Neurological dysfunction.

25. RADICULOPATHY False-localizing radiculopathy may occur in IIH and cerebral venous sinus thrombosis, manifesting as acral paresthesias , backache and radicular pain, and less often with motor deficits, which on occasion may be sufficiently extensive to mimic GBS. Mechanism: Root compression due to elevated CSF Pressure.

26. CEREBELLAR SYNDROME Damage to Fronto-ponto-cerebellar pathway, e.g. as a result of ACA territory infarction,  incoordination of the contralateral limbs, mimicking cerebellar dysfunction. Posterior fossa tumors  ataxia as “false localizing” sign- pt has headache and papilledema

27. PSEUDOATHETOSIS Abnormal writhing movements of the fingers, Worse on eye closure Caused by failure of proprioception along its pathway from peripheral nerve to parietal cortex. It may be mistaken for choreoathetosis , which is relatively constant irrespective of whether the eyes are open or closed.

28. OBTURATOR NEUROPATHY Obturator Neuropathy: Pelvic Malignancies- Many patients appear to have hip flexor weakness as a false localizing sign. May be explained by pain, but it is more likely due to mechanical disadvantage of the hip flexors in the presence of weak thigh adductors.

29. PSEUDOSYRINGOMYELIA Selective loss of pain and temperature sensation with relative preservation of vibration and position sense Seen in amyloid polyneuropathy and Tangier disease, both causes of Small Fibre Sensory Neuropathy.

30. IMPORTANCE Pose a clinical challenge – cannot be relied upon for localisation . Awareness of situations in which they are most likely to occur is necessary to heighten clinical suspicion. May indicate life-threatening pathology.