What is the management approach for a 40-year-old female with myasthenia gravis (MG) who develops a lower respiratory tract infection (LRTI)?

Management of Lower Respiratory Tract Infection in a 40-Year-Old Female with Myasthenia Gravis

This patient requires immediate hospital admission due to the high risk of myasthenic crisis triggered by respiratory infection, which is the most common precipitant of respiratory failure in MG patients. 1, 2

Immediate Risk Assessment and Hospital Admission

Respiratory infections are the most frequent trigger of myasthenic crisis (MC), occurring in 15-20% of MG patients, typically within the first 2-3 years of disease. 1, 2 This patient meets criteria for hospital admission based on:

• Presence of myasthenia gravis itself constitutes a neurological comorbidity requiring hospital referral for LRTI 3
• Risk of rapid deterioration to respiratory failure within minutes to days 2
• Need for close monitoring of bulbar and respiratory muscle function 2, 4

The European Respiratory Society identifies specific signs requiring immediate hospital admission: temperature <35°C or ≥40°C, heart rate ≥125 beats/min, respiratory rate ≥30 breaths/min, cyanosis, blood pressure <90/60 mmHg, confusion, or altered mental status 3, 5

Critical Initial Workup

Upon admission, perform the following assessments immediately:

• Pulmonary function testing with negative inspiratory force (NIF) and vital capacity (VC) to quantify respiratory muscle strength 3
• Arterial blood gases or pulse oximetry (hypoxemia with PaO₂ <60 mmHg or hypercapnia with PaCO₂ >50 mmHg indicates severe disease) 3
• Chest radiograph (posteroanterior and lateral) to assess for multilobar involvement, pleural effusion, or cavitation 3
• Complete blood count, serum biochemistry (sodium, potassium, glucose, urea, creatinine) 3
• Sputum Gram stain and culture (only interpret if >25 polymorphonuclear cells and <10 squamous epithelial cells per high-power field) 3
• Blood cultures before antibiotic initiation 6

Antibiotic Selection: Critical Medication Considerations

Avoid fluoroquinolones and macrolide antibiotics as they can worsen myasthenia gravis. 3 The ASCO guideline explicitly states to "review and stop medications with known risk of worsening myasthenia: beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics." 3

For Hospitalized Patients (Non-ICU):

Use second or third-generation cephalosporins as first-line therapy:

• IV cefuroxime 750-1500 mg every 8 hours 5
• IV ceftriaxone 1 g daily 5, 6
• IV cefotaxime 1 g every 8 hours 5

Alternative if beta-lactam allergy: IV aztreonam plus IV azithromycin (though azithromycin is a macrolide, it may be necessary in severe allergy cases with close monitoring) 6

For ICU-Level Severity:

Combination therapy with second or third-generation cephalosporin PLUS a second-generation quinolone (despite MG concerns, this may be necessary in life-threatening situations with close monitoring) 5

Treatment duration: 7-10 days for uncomplicated bacterial LRTI 3

Management of Myasthenia Gravis During LRTI

Anticholinesterase Medication:

• Continue pyridostigmine during stable LRTI 7
• If respiratory failure develops requiring mechanical ventilation, interrupt anticholinesterase medication temporarily 8
• Pyridostigmine dosing: start 30 mg PO three times daily, gradually increase to maximum 120 mg four times daily based on symptoms 3

Immunotherapy Considerations:

If signs of impending myasthenic crisis develop (progressive bulbar symptoms, declining respiratory function):

• Plasmapheresis is preferred over IVIG for myasthenic crisis 1, 2, 8
• IVIG 2 g/kg IV over 5 days (0.4 g/kg/day) as alternative 3
• Initiate or optimize corticosteroids (prednisone 0.5 mg/kg orally daily) 3, 2

ICU Transfer Criteria

Transfer to ICU immediately if any of the following develop:

• Respiratory rate >30 breaths/min 3, 9
• PaO₂/FiO₂ <250 mmHg or need for mechanical ventilation 6, 9
• Progressive bulbar weakness with aspiration risk 2, 4
• Declining NIF or VC on serial measurements 3
• Systolic blood pressure <90 mmHg or diastolic <60 mmHg 9
• Altered mental status or confusion 3, 9

Monitoring Protocol

Daily assessments must include:

• Serial pulmonary function testing (NIF and VC) 3
• Clinical evaluation for bulbar symptoms (dysphagia, dysarthria, aspiration risk) 2, 4
• Respiratory rate, oxygen saturation, work of breathing 3
• Response to antibiotic therapy (fever should resolve within 48 hours) 3

Median duration of myasthenic crisis requiring mechanical ventilation is 12-14 days, though 20% remain ventilated after 1 month 2

Common Pitfalls

• Do not use macrolides (clarithromycin, azithromycin) or fluoroquinolones as first-line therapy in MG patients 3
• Do not delay hospital admission—respiratory deterioration can occur within minutes to hours 2
• Do not wait for respiratory failure to develop before initiating immunotherapy if progressive weakness is evident 2, 4
• Do not increase pyridostigmine dosing if weakness worsens—this may indicate cholinergic crisis rather than myasthenic crisis 7
• Mortality in myasthenic crisis is <5% when managed appropriately but rises significantly with delayed recognition 1