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  1. 1. Introduction to Localization in Neurology Precase Information Jill Cramer, M.D. February 26, 2007 One of the most important clinical skills in neurology is the ability to localize a lesion. When you first approach a neurological condition, first localize, then derive your differential diagnosis to help drive your evaluation and ultimate diagnosis of the patient. Refer to this outline to help localize lesions in neurology. Consider this outline as you learn about the individual neurological pathways and anatomical structures during this block. When a patient has neurological deficits that localize to a single point in the nervous system, particularly to the brain or spinal cord, we refer to these deficits as “focal neurological deficits.” Symptoms and signs that present all over the body are referred to as “generalized neurological deficits.” This distinction is very useful as you try to localize the lesion. I. General Concepts in Localization a. Terminology i. Dermatome – area of skin innervated by a particular nerve root’s sensory fibers ii. Myotome – muscle groups innervated by a particular nerve root’s motor fibers iii. Anterior horn – anterior and lateral region of the spinal cord, where motor nerve fibers gather together to leave the spinal cord iv. Posterior columns – Posterior and medial region of the spinal cord, where vibratory and proprioception signals are primarily located v. Aphasia – dysfunction of language vi. Dysarthria – slurred speech (note the difference between dysarthria and aphasia) vii. Dysphagia – difficulty swallowing b. Focal vs. generalized signs and symptoms i. Focal signs and symptoms localize to a particular place in the nervous system; for example… 1. Aphasia 2. Focal weakness (one side of the body or one limb) 3. Double vision ii. Generalized signs and symptoms are either nonspecific or involve the diffuse areas of the nervous system; for example… 1. Dysarthria 2. Generalized weakness (both sides of the body WITHOUT a spinal sensory level that would indicate myelopathy) 3. Generalized confusion 4. Blurry vision 5. Lightheadedness c. Upper vs. lower motor neuron signs i. Upper motor neuron – CNS – brain and spinal cord 1. Increased tone, spasticity 2. Increased reflexes 3. Arms – flexors stronger than extensors; legs – extensors stronger than flexors ii. Lower motor neuron – PNS – peripheral nerves 1. Muscle fasciculations (small twitches in the muscles) 2. Muscle atrophy 3. Muscle cramping d. Know where the clinically important tracts cross i. Corticospinal (motor) tract crosses in the pyramidal decussation, in the medulla
  2. 2. 1. Lesions below the medulla will cause IPSILATERAL weakness 2. Lesions above the medulla will cause CONTRALATERAL weakness ii. Spinothalamic (pain and temperature) tract crosses 2-3 spinal segments above the entry point into the spine 1. Lesions at a given spinal level will cause CONTRALATERAL pain and temperature sensation loss starting 2-3 dermatomal segments below the level of the lesion II. Brain – Look for face and limb symptoms, alteration in consciousness, seizures, trouble creating or understanding language a. Cortical – Look for contralateral face, arm, and leg weakness and numbness, language deficits, and visual field cut i. Anterior Cerebral Artery distribution 1. Contralateral leg weakness and numbness ii. Middle Cerebral Artery distribution 1. Contralateral face, arm, and leg weakness and numbness 2. Language disturbance, specifically aphasia – temporal lobe = trouble understanding language; frontal lobe = trouble creating language 3. Visual field cut may be present – the patient cannot see out of either eye on the side contralateral to the lesion 4. Gaze preference; the patient looks toward the lesion and cannot move the eyes away from the lesion iii. Posterior Cerebral Artery distribution 1. Visual field cut contralateral to the lesion; macular visual area often spared 2. Alexia without agraphia (upper posterior temporal lobe); the patient cannot read but can write b. Subcortical – Look for contralateral face, arm, and leg weakness and numbness i. Internal capsule 1. Pure motor hemiplegia contralateral to the lesion 2. Pure hemisensory deficit contralateral to the lesion ii. Thalamus 1. Pure hemisensory deficit contralateral to the lesion 2. May have language disturbance, gaze preference, and other cortical signs very similar to a cortical lesion III. Brainstem – Look for cranial nerve deficits and/or face deficits ipsilateral to the lesion and limb deficits contralateral to the lesion; this difference between facial and limb findings is called “crossed” neurological deficits. a. Midbrain i. Deficits of ocular motility; symptoms may include double vision ii. Limb and/or gait ataxia iii. Hemiplegia contralateral to the lesion b. Pons i. Facial weakness ipsilateral to the lesion; the patient can usually not raise both eyebrows, as the lesion presents as a “lower motor neuron” pattern on examination (looks like Bell’s palsy) ii. Dysarthria (this symptom can also be a sign of generalized dysfunction and is not specific to pontine lesions) iii. Pupillary changes c. Medulla i. Vertigo, nausea, vomiting, voice hoarseness ii. Dysphagia iii. Ipsilateral loss of taste due to CN VII nucleus lesion iv. Ipsilateral arm clumsiness
  3. 3. v. Ipsilateral facial sensory loss vi. Contralateral body proprioception deficits with intact light touch, vibration, proprioception vii. Ipsilateral Horner’s syndrome (CN III involved – ptosis, pupil constricted) IV. Cerebellum – Look for problems with movement without weakness (unless other structures are involved) a. “Scanning” speech pattern – monotonous, irregular cadence b. Ipsilateral limb ataxia which causes gait ataxia c. Speech dysarthria, dysphagia d. Conjugate but uncoordinated eye movements e. Lateral cerebellar lesions typically affect the upper limbs; central cerebellar lesions typically affect the trunk, lower limbs and gait V. Spinal cord – Look for usually severe limb dysfunction in the absence of cranial nerve findings a. Bowel and bladder dysfunction – often incontinence b. Brown –Sequard syndrome results from a lesion to half of the spinal cord causes ipsilateral weakness and increased reflexes with contralateral pain and temperature dysfunction c. Transverse myelitis results from transecting lesion of the entire cord causes bilateral lower extremity weakness with loss of or decreased sensation from one point downward on the body. The loss of sensation from one point downward is known as a “spinal sensory level” and is highly suggestive of a spinal cord injury. d. Central syrinx (usually in the cervical or upper thoracic cord) causes a “cape-like” pattern of weakness and numbness across the upper extremities (because spinothalamic tracts cross near the central syrinx and are compressed at the affected levels) with increased reflexes, weakness, and spasticity in the lower extremities e. Notable spinal cord levels i. The level of the nipples is at T4 ii. The umbilicus is at T10 VI. Anterior horn cell – Look for isolated upper motor neuron findings and usually progressive motor symptoms throughout the body, all limbs, without sensory changes. a. Weakness, limb spasticity, increased reflexes b. Muscle fasciculations, cramps VII. Peripheral nerves – Look for lower motor neuron signs in motor lesions and either diffuse sensory loss or focal sensory loss that follows a particular nerve’s distribution a. Nerve root (radiculopathy) i. Pain and numbness in the dermatome supplied by the nerve root ii. Weakness in the myotome supplied by the nerve root b. Local (mononeuropathy) i. Focal weakness and/or numbness in the distribution of the affected nerve c. Diffuse (polyneuropathy or peripheral neuropathy) i. Numbness or paresthesias in bilateral hands and feet (“stocking glove” distribution); may affect one side more than the other ii. Weakness is typically distal iii. Ascending pain, numbness, and weakness (as in Guillain-Barre syndrome) VIII. Neuromuscular junction – Look for fluctuating weakness and muscle wasting a. Myasthenia gravis produces worsening double vision, ptosis, and weakness with exercise b. Lambert-Eaton syndrome produces improving weakness with exercise IX. Muscle – Look for weakness without sensory changes a. Proximal weakness without sensory changes b. Pain in the muscles may be present c. Myositis is often associated with skin rash, alopecia, and joint pain and swelling d. Hereditary myopathies are associated with exercise intolerance and progressive weakness
  4. 4. Introduction to Localization in Neurology Precase Questions Jill Cramer, M.D. February 26, 2007 As you go through the precase questions, keep in mind all of the potential regions of the nervous system where a lesion may localize. Although exam questions typically have five multiple choices, the “real world” presents essay-type questions. Always think through all of the possibilities when trying to localize a lesion. Your choices are a. Right cerebral hemisphere b. Left cerebral hemisphere c. Right internal capsule (subcortical) d. Left internal capsule (subcortical) e. Right brainstem f. Left brainstem g. Cerebellum h. Spinal cord i. Anterior horn j. Peripheral nerves k. Neuromuscular junction l. Muscle m. These are generalized symptoms; it is not possible to localize the lesion 1. A 36 year old woman presents with acute onset inability to speak, left facial droop, left arm and leg weakness, and inability to look to the left (this is also know as right gaze preference). Where does this lesion localize? a. Right cerebral hemisphere b. Right internal capsule (subcortical) c. Right brainstem d. Spinal cord e. Neuromuscular junction 2. A 72 year old man with known hypertension and diabetes presents with a 2-day history of lightheadedness, blurry vision, and confusion. Examination reveals diffuse weakness in all limbs, difficulty maintaining arousal, and trouble following all commands without ongoing prompting and reminding. Where does this lesion localize? a. Left cerebral hemisphere b. Right brainstem c. Peripheral nerves d. Muscle e. These are generalized symptoms; it is not possible to localize the lesion 3. A 14 year old boy presents with progressively worsening difficulty participating in gym classes due to easy fatigue. Examination reveals weakness in hip flexor muscles and in shoulder girdle muscles. Reflexes are normal. There are no sensory changes. Where does this lesion localize? a. Spinal cord b. Anterior horn c. Peripheral nerves d. Muscle e. These are generalized symptoms; it is not possible to localize the lesion
  5. 5. 4. A 56 year old man presents after a motor vehicle accident in which he sustained a whiplash injury. Examination reveals loss of pain and temperature sensation across the shoulders and into both arms. Arms are strong. Both legs are weak. Reflexes in the arms are normal; reflexes in the legs are increased. Where does this lesion localize? a. Brainstem b. Spinal cord c. Anterior horn d. Neuromuscular junction e. Muscle 5. A 66 year old woman presents with intermittent eyelid droop and double vision. She finds that both arms become heavy when she crochets for long periods of time. The heaviness improves if she rests. There is no associated numbness or pain. Where does this lesion localize? a. Anterior horn b. Peripheral nerves c. Neuromuscular junction d. Muscle e. These are generalized symptoms; it is not possible to localize the lesion