Approach to Ataxia and Gait Disorders

Question 1

Things that should generally make you think “ataxia” on exam

Answer 1

• Dysarthria
• Dysmetria
• Dysdiadochokinesia
• Gait ataxia
• Intention tremor (specifically towards the end of a voluntary movement)
• Nystagmus
• Truncal ataxia (oscillatory movements of the trunk while standing)
• Pseudoathetosis (Involuntary, slow, writing movements of the digits that occur only when the eyes are closed)

Question 2

Athetosis vs pseudoathetosis

Answer 2

Athetosis: Involuntary, slow, writing movements of the digits. Usually a sign of basal ganglia dysfunction, often seen in Huntington’s, cerebral palsy, or post-basal ganglia stroke.

Pseudoathetosis: Involuntary, slow, writing movements of the digits that occur only when the eyes are closed. An ataxic sign that often localizes to the cerebellum or dorsal column.

Question 3

Acute onset unilateral or truncal ataxia should ALWAYS make you think of. . .

Answer 3

. . . cerebellar stroke

Question 4

Postinfectious cerebellitis

Answer 4

• An acute-to-subacute onset ataxic syndrome typically affecting children ages 2-7
• Follows a viral infection, especially varicella
• Symptoms:
  
  • Dysmetria
  • Gait ataxia
  • Dysarthria
  • Fever
  • N/V
  • Headache
• Resolves spontaneously over weeks with supportive therapy. Antivirals and steroids are often used for treatment as appropriate.

Question 5

Miller Fisher syndrome

Answer 5

• Triad of ataxia, areflexia, and ophthalmoplegia
• Often a post-infectious process
• Thought of as a variant of Gullian-Barre syndrome
• Diagnosis: Mediated by anti-GQ1b antibodies
  
  • These are found in the serum of over 90% of patients with this disorder
• Treatment: Responds well to IVIG

Question 6

Paraneoplastic cerebellar degeneration

Answer 6

• Caused by the development of autoantibodies
• Symptoms are cerebellar (nystagmus, dysarthria, gait/limb/truncal ataxia)
• Onsets acutely to subacutely
• Often precedes the diagnosis of the causative malignancy
• Most associated cancers: Ovarian, small cell lung cancer
• Diagnosis:
  
  • Search for cancer
  • Serology for antibodies (of which there are many, but anti-Yo is most common. Only ~65% sensitive)
• Treatment:
  
  • Treat underlying cancer
  • Immunosuppression (IVIG, rituximab)

Question 7

Friedrich ataxia

Answer 7

• Slowly progressive multisystem disorder
• Most common form of hereditary ataxia
• Caused by a trinucleotide repeat expansion in the frataxin gene
• Clinical course:
  
  • Presents in childhood with gait ataxia
  • Progresses to involve the trunk and arms
  • Reflexes are lost, neuropathy develops, and toes are upgoing
• Syndrome also involves:
  
  • Cardiomyoptahy
  • Diabetes
  • Hearing loss

Question 8

Episodic ataxia

Answer 8

• Characterized by recurrent, brief episodes of ataxia, vertigo, N/V, with complete resolution of symptoms between spells
• Presents in early childhood
• Myokymia (muscle twitching) may be observed in patients with EA type 1
• Interictal nystagmus and mild baseline ataxia may be observed in patients with EA type 2
• Caused by mutations in ion channels:
  
  • KCNA1 (EA-1, voltage gated potassium channel)
  • CACNA1A (EA-2, voltage gated calcium channel, also the cause of SCA-6)
• Treatment: Acetazolomide reduces the frequency of attacks

Question 9

CACNA1A

Answer 9

• Encodes the Ca_V2.1 voltage-dependent calcium channel
• Mutations in this gene cause both familial SCA-6 and familial EA-2