What tests should be done for a patient with Multiple Sclerosis (MS) experiencing Shortness of Breath (SOB)?

Diagnostic Tests for Multiple Sclerosis Patients with Shortness of Breath

For MS patients experiencing shortness of breath, pulmonary function testing (PFT) should be performed to assess respiratory muscle function, along with evaluation for dysphagia and cardiac causes, as these are the most common contributors to SOB in this population. 1, 2

Respiratory Assessment

Pulmonary Function Testing

• Perform complete pulmonary function tests including vital capacity (VC), maximum voluntary ventilation (MVV), and respiratory muscle strength measurements (PImax and PEmax) 1
• MS patients commonly show decreased maximum voluntary ventilation (MVV) and respiratory muscle weakness, particularly affecting expiratory muscles, even when lung volumes appear normal 2, 3
• Restrictive respiratory failure is frequent in severely impaired MS patients, with vital capacity often reduced to approximately 58% of predicted values 2

Clinical Respiratory Muscle Assessment

• Use a systematic clinical assessment index that includes:
  • Patient's report of difficulty clearing pulmonary secretions
  • Patient's report of weakened cough
  • Examiner's observation of patient's cough
  • Patient's ability to count on a single exhalation 1
• This clinical assessment is a better predictor of respiratory muscle weakness than spirometry alone 1

Dysphagia Evaluation

Dysphagia Screening

• All MS patients with SOB should be screened for dysphagia, as it affects 36-81% of MS patients and can contribute to respiratory symptoms 4
• Use the Dysphagia in Multiple Sclerosis (DYMUS) questionnaire, which includes 10 questions assessing dysphagia for solids and liquids 4
• Highest risk patients include those with:
  • Severe disabilities
  • Cerebellar dysfunction
  • Long disease duration 4

Instrumental Dysphagia Assessment

• Perform instrumental exploration (FEES or videofluoroscopy) in high-risk patients or those with dysphagia symptoms 4
• Common findings include pharyngeal stage disorders (28.7%), aspiration (6.9%), and oral stage disorders (5%) 4

Cardiac Evaluation

Echocardiography

• Transthoracic echocardiography (TTE) should be performed in MS patients with unexplained SOB to evaluate for cardiac causes 4
• TTE helps identify or exclude:
  • Heart failure (preserved, mid-range, or reduced ejection fraction)
  • Valvular heart disease (particularly mitral stenosis which can present with SOB)
  • Cardiomyopathies 4
  • Pulmonary hypertension (common in MS patients with respiratory involvement) 4

Exercise Testing

• Consider hemodynamic exercise testing with Doppler echocardiography for sedentary MS patients to assess objective limitations 4
• This is particularly important if pulmonary hypertension is suspected (pulmonary artery systolic pressure >50 mm Hg) 4

Additional Considerations

Sleep Evaluation

• Consider evaluation for sleep-disordered breathing in MS patients with SOB, especially if symptoms are worse at night or upon awakening 4
• Up to 70% of MS patients may experience nocturnal oxygen desaturation (SaO2 <92%) 3

Medication-Related Causes

• Review current medications, particularly interferon β-1b therapy, which has been associated with nephrotic syndrome that can present with SOB 5

Differential Diagnosis

• Consider vasculitic disorders that can mimic MS and cause respiratory symptoms, such as Churg-Strauss syndrome, especially in patients with atypical MS presentation and asthma 6

Pitfalls and Caveats

• Respiratory dysfunction in MS is often underdiagnosed as symptoms may be attributed to deconditioning or fatigue 2
• Standard spirometry alone may miss significant respiratory muscle weakness; always include respiratory muscle strength testing 1
• Expiratory muscle weakness is more common than inspiratory weakness in MS, affecting cough efficacy and secretion clearance 2
• The severity of respiratory dysfunction correlates with overall disability (EDSS score) but can occur even in patients with mild neurological impairment 3