Differential Diagnosis in Neurology

13.1. Anatomy and Anatomically Based Syndromes

Cerebellar Disease

• General considerations:
  • The cerebellum is parcellated both anatomically and functionally into specific zones.
    • The archicerebellum consists of the flocculonodular lobe; it has major connections with the vestibular system and is important for control of eye movements.
    • The paleocerebellum is composed of the vermis of the anterior lobe (lobule I-V) as well as the pyramis, uvula and paraflocculus. Most of its afferents are from the spinal cord. Its major functional role involves muscle tone and control of axial and limb movements.
    • The neocerebellum comprises the middle vermis and the hemispheres.
    • The cerebellar cortex may be divided into longitudinal zones that project to specific nuclei.
      • The vermal zone projects to the fastigial nucleus
      • The intermediate zone projects to the nucleus globosus and emboliformis
      • The lateral zone projects to the dentate nucleus
    • The somatotopic representation within each nucleus is:
      • Caudal body parts are anterior; rostral parts posterior, trunk is lateral; limbs medial.
    • Functional anatomy of the nuclei:
      • Fastigial nucleus
        • Upright posture, muscles of the trunk
        • Important for sitting, standing and walking
      • The globosus and emboliform nuclei:
        • Involved with segmental reflexes that control stability
        • Important for the initiation of movements derived from somatosensory input (proprioception)
        • Stabilizes proximal joints that facilitate pyramidal movements
        • Lesions cause:
          • Delayed check
          • Truncal titubation
          • Oscillation of the extremities
        • Facilitate control of oscillations during the last 1/3 of movement.
      • The dentate nucleus
        • Important in the facility of fine movement by promoting their initiation, coordinating extensor and flexor musculature at multiple joints, controlling the spatial coordination of hard and finger movements. Lesions of the nucleus and its connections cause postural kinetic tremors (rubral tremor). This tremor is distinguished by increasing amplitude of oscillation that occurs at right angles to the line of movement

The Afferent and Efferent Cerebellar Pathways of Clinical Relevance

• Inferior Cerebellar Peduncle
  • This is known as the restiform body and is most often involved in vertebral artery and PICA strokes, as well as by compression from tumors, demyelinating disease and stroke.

Tracts of the Inferior Cerebellar Peduncle

• The dorsal spinal cerebellar tract which carries proprioceptive and exteroceptive information from the lower extremity and trunk. Cervical spondylosis and any spinal cord compressive disease, as well as the reviewed acquired and congenital diseases of the cervical cord affect this pathway. No patient with significant cervical stenosis from any cause can tandem walk. It originates from Clarke's column of the spinal cord.
• The cuneocerebellar tract that arises from the external arcuate nucleus and relays proprioceptive information from the arm and neck
• The vestibulocerebellar tract projects bilaterally to the flocculonodular lobe. A cause of cervical induced nystagmus.
• Reticulocerebellar tracts from the lateral and paramedian nuclei of the brainstem are important for tone and cerebellar influences on segmental reflexes
• The arcuate cerebellar tract arising from the medullary arcuate nuclei
• Trigeminocerebellar tract which originates in the spinal and main sensory nuclei of cranial nerve V. This nucleus is important for migraine, head pain, and facial reflexes (trigeminal reflexes, i.e., light causing cough)
• Olivocerebellar tract is an afferent tract for somatic modalities from the contralateral inferior olivary nucleus.

Efferent Tracts in the Inferior Cerebellar Peduncle

• Fastigiobulbar tract (juxtarestiform body) and cerebellar reticular efferents)

The Middle Cerebellar Peduncle (the Brachium Pontis)

The middle cerebellar peduncle (the brachium pontis) connects the cerebellum to the pons. Corticospinal fibers synapse in the pontine gray, project to the intermediate zone of the cerebellum and thence to the cerebellar zone of the thalamus in the ventrolateral nucleus. These afferents then project to area 3b of the somato sensory cortex and thence to area 4 of the primary motor cortex.

Lesions of this distributed pathway cause specific symptom complexes at each level of involvement.

Pontine grey lesions cause hemiparesis and ataxia of the contralateral side. Descending corticospinal fibers are responsible for the weakness and are the origin of the middle cerebellar peduncle (MCP) which projects to the intermediate zone of the cerebellum and then to the thalamus and cortex; a cause of ataxic gait.

The lateral zone of the cerebellum, if involved, causes greater ataxia of the arm then the leg as does involvement of the middle cerebellar peduncle. Thalamic lesions involving cerebellar radiations are notable for ataxia of stance. Disruptions of cerebellar connections from BA 3b of SI to M1 of BA 4 cause Brunn's frontal lobe ataxia.

The Superior Cerebellar Peduncle (SCP)

The superior cerebellar peduncle is the primary connection of the cerebellum to the midbrain. It is the primary efferent pathway of the cerebellum.

The clinically most important efferent pathways are the dentatorubral and dentothalamic tracts which are the anatomic basis of the postural kinetic and cerebellar outflow tremors, seen with midbrain and thalamic lesions.

Specific Anatomically Based Cerebellar Syndromes

Rostral Vermis Syndrome

• General considerations:
  • Most often seen in alcoholic patients
  • Anterior and superior vermis are involved (the lingula, centralis, culmen)
  • Severe Purkinje cell loss
• Clinical features:
  • "Martonette" gait; broad based with predominance of truncal extensor tone
  • Minimal arm ataxia
  • Minimal or no dysarthria and extraocular muscle impairment
  • No heel to shin ataxia in recumbency

Caudal Vermis Syndrome

• General considerations:
  • Primary damage is to the floccular nodular lobe
  • Medulloblastoma in children
  • Posterior fossa cysts and hemorrhages, Chiari malformations are most common in adults
• Clinical features:
  • Titubation; inability to sit with the back straight
  • Minimal limb ataxia
  • Extraocular movements:
    • Down-beat nystagmus accentuated in lateral gaze
    • Rotary nystagmus
    • Hypermetric saccades

Posterior Vermal Split Syndrome

• General considerations:
  • Caused by surgical disruption of parallel fibers crossing the midline cerebellar cortex
• Clinical features:
  • Severe difficulty in performing tandem gait
  • Normal regular gait, standing and unilateral hopping

Cerebellar Hemispheric Syndrome

• General considerations:
  • Usually caused by metastases, abscesses and infarction
  • Muscles controlled by the precentral cortex are primarily affected
• Clinical features:
  • Poor fine finger movement and incoordination of the ipsilateral extremity
  • Dysarthria

Pan Cerebellar Syndrome

• General considerations:
  • Signs and symptoms of all cerebellar syndromes
  • Caused by autoimmune and infectious processes, hypoglycemia, paraneoplastic induced antigens (anti-Yo and anti-Hu), hyperthermia, solvents, toxins and hypothyroidism
• Clinical features:
  • Bilateral signs of cerebellar dysfunction that is appendicular and truncal
  • Extraocular movements are affected

Differential Diagnosis of Major Cerebellar Arterial Diseases

• PICA
  • The distinguishing features of a PICA infarction are nausea, vomiting, hoarseness, rotary nystagmus to the side of the lesion and inability to walk out of proportion to other aspects of the stroke. A pure medial branch occlusion may primarily involve the nucleus ambiguous. A pure lateral lesion may cause isolated vertigo and dysmetria without dysarthria and without vestibular signs. The sensory loss is to pain and temperature of the ipsilateral face and contralateral body.
• AICA
  • The hallmark of an AICA occlusion is sudden hearing loss, a peripheral facial (a branch of the artery, supplies the VIIth nerve peripherally) and ataxia of the arm greater than the leg.
• Superior cerebellar artery
  • The superior cerebellar artery is frequently infarcted by an embolus to the top of the basilar artery. The occlusion is manifest by ataxia of all extremities and severe dysarthria. These features are often accompanied by midbrain, thalamic and parietal signs and symptoms. The interpeduncular artery from the top of the basilar feeds the decussation of the SCP at the level of the inferior colliculus (Windekink's commissure) which can also cause ataxia of all extremities. Rarely, patients have a contralateral IVth nerve and hearing loss (crossed fibers of the lateral lemniscus).

Oculomotor Deficits of Superior Cerebellar Artery Occlusion

• Contrapulsion of saccadic eye movements. These complex eye movements have three major components:
  • Horizontal saccades away from the lesion (opposite side) on upgaze which causes an oblique trajectory of the nystagmus
  • Hypermetria of the contralateral saccadic movement
  • Hypometria of ipsilateral saccades
• These eye movements are opposite to those seen with PICA infarction
  • Lateral pulsion to the side of the lesion (torsional nystagmus on attempted upgaze)
  • Hypometric saccades contralaterally.

Lateral branch of the superior cerebellar artery signs and symptoms

• Ipsilateral extremity dysmetria
• Axial lateral pulsion (ipsilaterally)
• Contra pulsion of saccades
• Dysarthria
• Clumsy hand dysarthria syndrome

Medial Branch Cerebellar Artery Infarction

• Dysarthria and gait abnormalities are the most prominent feature
• Rarely ipsilateral appendicular dysmetria, extensor posturing of the trunk and all extremities.