What is the diagnosis and management for a 21-year-old patient with a history of swaying while walking since childhood, subsequent development of slurring of speech, and examination findings of gait ataxia, limb ataxia, scanning speech, gaze-evoked nystagmus, pes cavus, finger deformity, hammer toes, kyphoscoliosis, and facial myokymia, with cerebellar atrophy on MRI and negative genetic testing for Friedreich's ataxia?

Diagnosis: Spinocerebellar Ataxia (SCA)

This patient most likely has an autosomal dominant spinocerebellar ataxia (SCA), given the childhood-onset progressive cerebellar syndrome with skeletal deformities, cerebellar atrophy on MRI, and negative Friedreich's ataxia genetic testing. 1

Diagnostic Reasoning

Why This is NOT Friedreich's Ataxia

• Friedreich's ataxia typically presents with absent tendon reflexes in the legs, limb and truncal ataxia as the only consistent early diagnostic criteria within five years of presentation 2
• The presence of facial myokymia is not characteristic of Friedreich's ataxia and points toward other SCA subtypes 2
• Friedreich's ataxia shows preserved cerebellar volume on MRI, whereas this patient has cerebellar atrophy 3
• Genetic testing has already excluded Friedreich's ataxia 1

Why This is Likely SCA

• Spinocerebellar ataxias represent genetically heterogeneous autosomal dominant neurodegenerative disorders with variable phenotypic expression and progressive cerebellar hemispheric and vermian volume loss 1
• The childhood onset with progressive gait ataxia, dysarthria, skeletal deformities (pes cavus, kyphoscoliosis), and cerebellar atrophy on MRI are classic for inherited SCAs 1, 4
• Facial myokymia can occur in certain SCA subtypes, distinguishing this from Friedreich's ataxia 5
• The gaze-evoked nystagmus with broken pursuits and scanning speech are characteristic cerebellar examination findings 5

Recommended Diagnostic Workup

Genetic Testing Priority

• Proceed with comprehensive genetic panel testing for spinocerebellar ataxias, focusing on the common autosomal dominant SCAs (SCA1, SCA2, SCA3, SCA6, SCA7) which are due to genetic repeat expansions 4
• Consider expanded genetic testing including next-generation sequencing panels if initial common SCA testing is negative, as there are many genetically heterogeneous causes 1

Additional Imaging

• MRI of the cervical and thoracic spine without contrast should be obtained to evaluate for spinal cord atrophy, which has been described in SCA1, SCA7, and other subtypes and correlates with symptom severity 6
• The presence of motor spasticity or sensory ataxia would further support the need for spine imaging 6

Metabolic and Acquired Causes to Exclude

• Vitamin E deficiency must be excluded as it can cause cerebellar involvement with spinal cord pathology and skeletal deformities 7
• Check serum vitamin E levels, lipid profile, and consider testing for abetalipoproteinemia 7
• Exclude inflammatory disorders and paraneoplastic syndromes, as these are treatable causes that affect mortality 1

Management Approach

Symptomatic Treatment

• Balance training programs can improve stability in patients with cerebellar ataxia 5
• Postural training can improve trunk control 5
• Task-oriented upper limb training can improve reaching and fine motor control 5
• Prescription of appropriate assistive devices and orthoses can improve balance and mobility, particularly given the skeletal deformities present 5

Monitoring and Complications

• Serial MRI imaging may be necessary to demonstrate progression, as early imaging in hereditary cerebellar ataxias may be normal or subtly abnormal, with abnormalities becoming more apparent on follow-up 1
• Cardiac evaluation with ECG and echocardiography should be performed, as cardiomyopathy can occur in certain SCAs 2
• Monitor for development of diabetes mellitus, which clusters in some hereditary ataxias 2

Genetic Counseling

• Family members should be offered genetic counseling and testing once the specific mutation is identified, as most SCAs follow autosomal dominant inheritance with variable penetrance 1, 4

Critical Pitfalls to Avoid

• Do not assume all progressive ataxia with negative Friedreich's testing is benign hereditary disease—always exclude tumors, inflammatory conditions, and paraneoplastic syndromes first, as these are treatable and affect mortality 1
• Do not overlook vitamin E deficiency, which is a treatable cause of progressive ataxia with skeletal deformities 7
• Do not miss associated spinal cord signs (motor spasticity, sensory ataxia) that would warrant spine imaging in addition to brain imaging 5
• The presence of cerebellar atrophy on MRI distinguishes this from Friedreich's ataxia, where cerebellar volume is typically preserved 3