What laboratory tests are indicated for a patient presenting with weakness, diplopia (double vision), vertigo (dizziness), and hypoxemia (low SpO2)?

From the Guidelines

For a patient presenting with weakness, double vision, dizziness, and low oxygen saturation (SpO2), I strongly recommend initiating a comprehensive laboratory workup including complete blood count (CBC), comprehensive metabolic panel (CMP), arterial blood gas (ABG), thyroid function tests, B12 and folate levels, and creatine kinase, as these tests are crucial in identifying the underlying cause of the patient's symptoms and guiding further management. The CBC will assess for anemia or infection which could explain weakness and low SpO2, as indicated by the need for blood gas estimations in chronically hypoxaemic patients 1. The CMP evaluates electrolyte imbalances (particularly potassium, calcium, and sodium) that may cause muscle weakness and neurological symptoms. An ABG is crucial to determine the cause of low SpO2 and identify acid-base disturbances, with a PaO2 of <7 kPa equating to SpO2 below ∼85% 1. Thyroid function tests are important as both hypo- and hyperthyroidism can cause weakness and neurological symptoms. B12 and folate deficiencies can lead to neurological manifestations including weakness and vision changes. Creatine kinase helps identify muscle breakdown. Additional tests to consider include myasthenia gravis antibodies if bulbar symptoms are prominent, and D-dimer if pulmonary embolism is suspected as a cause of low SpO2, although the positivity rate of head CT in the emergency department for patients presenting with dizziness or vertigo is very low, approximately 2% 1. These tests provide a foundation for diagnosis, though clinical context may necessitate additional specialized testing based on the patient's specific presentation and history, such as the use of Dix-Hallpike testing or conventional diagnostic angiography (DA) in specific subsets of patients presenting with episodic vertigo 1.

Some key points to consider in the management of this patient include:

• The importance of continuous monitoring of oxygen saturation until the patient is stable or arrives at hospital for a full assessment 1
• The need for a clear history of asthma or heart failure or other treatable illness, and institution of appropriate treatment in accordance with guidelines or standard management plans for each disease 1
• The potential use of portable pulse oximeters to assess hypoxaemia and guide use of oxygen if available, and the importance of calling emergency services if hypoxaemia or other serious illness is suspected 1
• The consideration of chronic disequilibrium with signs of cerebellar ataxia and sensory/proprioceptive ataxia, and the potential use of brain PET using various radiotracers to detect presymptomatic neuronal dysfunction in patients with certain types of spinocerebellar ataxia (SCA) 1

From the Research

Laboratory Tests for Weakness, Diplopia, Vertigo, and Hypoxemia

The patient's symptoms of weakness, diplopia, vertigo, and hypoxemia require a comprehensive diagnostic approach. The following laboratory tests and examinations are indicated:

• Complete Blood Count (CBC) to rule out anemia or infection 2
• Basic Metabolic Panel (BMP) to evaluate electrolyte imbalances and renal function 2
• Arterial Blood Gas (ABG) analysis to assess oxygenation and acid-base status
• Electrocardiogram (ECG) to evaluate cardiac function
• Imaging studies such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) to rule out stroke or other central nervous system abnormalities 3, 4, 5
• Neurological examination, including the three-component HINTS Test (Head Impulse, Nystagmus, and Test-of-Skew), to differentiate central from peripheral causes of vertigo 4, 5
• Dix-Hallpike and supine roll test to diagnose benign paroxysmal positional vertigo (BPPV) 5

Differential Diagnosis

The patient's symptoms can be caused by various conditions, including:

• Vestibular disorders such as vestibular neuritis or benign paroxysmal positional vertigo (BPPV) 4, 5
• Central nervous system abnormalities such as stroke or transient ischemic attack (TIA) 3, 4, 5
• Cardiac conditions such as arrhythmias or heart failure
• Electrolyte imbalances or renal dysfunction 2
• Respiratory disorders such as chronic obstructive pulmonary disease (COPD) or pneumonia

Diagnostic Approach

A logical and evidence-based approach is necessary to diagnose the underlying cause of the patient's symptoms. This includes:

• Taking a thorough medical history to identify potential causes and triggers of symptoms
• Performing a focused physical examination, including neurological and cardiovascular assessments
• Ordering laboratory tests and imaging studies as indicated to rule out potential causes
• Using diagnostic algorithms and decision-making tools to guide the diagnostic process 4, 5