Ataxia is a neurological symptom characterized by a lack of voluntary coordination of muscle movements, which can manifest as an unsteady gait, slurred speech, or difficulty with fine motor skills. This incoordination arises from dysfunction in the nervous system, most frequently from damage or degeneration in the cerebellum, the brain’s coordination center. Because ataxia is a symptom and not a disease itself, doctors must follow a diagnostic process to determine the underlying cause, which could range from reversible conditions like vitamin deficiency to progressive genetic disorders. Identifying a treatable cause or providing a definitive diagnosis is crucial for managing the condition.
The Initial Clinical Assessment
The diagnostic journey begins with a comprehensive medical and family history, gathering details about the onset, progression, and associated symptoms of the incoordination. This information helps categorize the ataxia as acute, chronic, acquired, or potentially hereditary, guiding the subsequent testing strategy. A detailed neurological examination follows, focusing on assessing the patient’s balance, gait, coordination, and reflexes.
Doctors use specific observational tests to evaluate cerebellar function, such as examining the patient’s walking pattern for the characteristic wide-based gait. The finger-to-nose test requires the patient to alternately touch their own nose and the examiner’s finger, revealing dysmetria. The heel-to-shin test assesses lower limb coordination as the patient attempts to slide their heel smoothly down the opposite shin.
Balance is often checked using the Romberg test, where the patient stands with their feet together and eyes closed, testing their ability to maintain posture without visual input. The examination also includes looking for nystagmus, an involuntary, rapid eye movement, and evaluating speech for dysarthria, which presents as slurred articulation. These initial findings distinguish the movement disorder from others and point toward the likely location of the neurological problem.
Structural Imaging and Brain Scans
Once the clinical assessment confirms ataxia, imaging studies visualize the structure of the brain and spinal cord. Magnetic Resonance Imaging (MRI) is the most common and detailed test, providing high-resolution images of the central nervous system’s soft tissues. MRI is effective for detecting structural abnormalities that could be causing the incoordination.
The scans look for signs of cerebellar atrophy, the shrinkage of the cerebellum, which is common in many chronic ataxias. MRI can also identify acute causes, such as a stroke, bleeding, tumors, or lesions damaging the brain tissue. Certain patterns of atrophy or signal changes on the MRI can suggest a specific type of ataxia, such as the “hot cross bun” sign seen in some spinocerebellar ataxias.
Computed Tomography (CT) scans are sometimes used, particularly in acute cases like head injury, to quickly rule out conditions such as intracranial hemorrhage or a large mass. While less detailed than an MRI for soft tissue, a CT scan provides fast information about structural damage. The focus of all imaging is to locate physical damage to the brain, brainstem, or spinal cord.
Laboratory Tests to Rule Out Other Causes
Laboratory tests identify acquired or reversible causes of ataxia that may mimic neurological degeneration. These tests typically involve blood and urine samples, screening for metabolic, toxic, and autoimmune issues. Identifying a treatable underlying cause is a priority in the diagnostic process.
Blood tests commonly measure levels of specific vitamins, focusing on deficiencies in Vitamin E and Vitamin B12, as low levels can impair nerve function and cause ataxic symptoms. Thyroid function tests are also performed, since an underactive thyroid can contribute to coordination problems. The blood work also looks for markers of autoimmune diseases, such as those associated with celiac disease or paraneoplastic syndromes.
Urine and blood screens may be ordered for drug toxicity, heavy metal exposure, or chronic alcohol use, all known causes of acquired ataxia. If infection or inflammation is suspected, a lumbar puncture (spinal tap) may be performed to analyze the cerebrospinal fluid for abnormal cells or infectious agents. These lab tests exclude non-neurological conditions before pursuing specialized genetic investigations.
Identifying Inherited Ataxia Through Genetic Analysis
If the initial clinical assessment, imaging, and lab work fail to reveal an acquired or structural cause, the investigation turns to genetic analysis, especially when a family history of movement disorders exists. Genetic testing analyzes a patient’s DNA, usually from a blood sample, to search for mutations causing hereditary forms of ataxia.
The analysis looks for specific gene defects, such as nucleotide repeat expansions, which characterize many hereditary ataxias. These expansions involve a DNA sequence being repeated too many times within a gene. Identifying these mutations provides a definitive diagnosis of a specific hereditary condition, such as Friedreich’s ataxia or a form of Spinocerebellar Ataxia (SCA).
Gene panels are widely used, allowing doctors to test for dozens of known ataxia-causing genes simultaneously. However, since over 300 hereditary conditions can include ataxia, a negative result from a standard panel does not always exclude a genetic cause. Genetic testing provides certainty about the specific type of ataxia, which is important for understanding disease progression and for family planning.