What causes episodes of knee buckling when feeling tired or overwhelmed?

Knee Buckling Episodes Triggered by Fatigue or Emotional Stress

Episodes of knee buckling that occur specifically when tired or feeling overwhelmed are most consistent with paroxysmal kinesigenic dyskinesia (PKD), a neurological disorder where sudden movements trigger involuntary movements, particularly when precipitated by emotional stress or fatigue. 1

Primary Diagnostic Consideration: Paroxysmal Kinesigenic Dyskinesia

PKD should be at the top of your differential diagnosis when patients describe episodic knee buckling specifically triggered by:

• Emotional stress or feeling overwhelmed 1
• Fatigue states 1
• Sudden voluntary movements (standing up, starting to walk) 1

Key Clinical Features to Assess

• Episode duration: PKD attacks last <1 minute in over 98% of cases 1
• Frequency: Can range from several times yearly to >100 times daily, typically peaking during puberty 1
• Aura symptoms: 78-82% of PKD patients experience numbness, tingling, or muscle weakness before episodes 1
• Age of onset: Most commonly presents between 7-20 years of age 1
• Gender: Males are affected 2-4 times more frequently than females 1

Specific Triggers to Inquire About

Beyond fatigue and emotional stress, ask about:

• Sudden standing or starting to run 1
• Hyperventilation 1
• Stimulation by sounds or images 1
• Changes in movement speed or amplitude 1

Alternative Considerations Based on Context

If Patient Has Diabetes

Screen for diabetic peripheral neuropathy, which can cause muscle weakness and "buckling" sensations:

• Perform 10-g monofilament testing or Ipswich touch test 1
• Add pinprick, temperature, or vibration assessment 1
• Examine for foot deformities and vascular status 1

If Patient Has Cancer History

Evaluate for cancer-related fatigue and associated weakness:

• Use Brief Fatigue Inventory (BFI) if screening score ≥4/10 1
• Assess for treatable causes: anemia, thyroid dysfunction, cardiac dysfunction 1
• Consider neurocognitive assessment if cognitive impairment accompanies weakness 1

If Patient Has Peripheral Arterial Disease Risk Factors

Consider claudication, though this typically presents as:

• Fatigue/discomfort during exercise that resolves with rest 1
• Specific muscle group involvement (hip, buttock, thigh, or calf) 1
• This is less likely given your description of buckling with emotional stress 1

Diagnostic Workup Algorithm

Initial Assessment

1. Detailed episode characterization: Duration, frequency, specific triggers, presence of aura 1
2. Neurological examination: Focus on motor strength, reflexes, sensory function 2
3. Screen for reversible causes: Anemia, thyroid dysfunction, electrolyte disturbances 3

When to Pursue PKD Diagnosis

If episodes are:

• Brief (<1 minute) 1
• Triggered by sudden movements AND emotional stress/fatigue 1
• Associated with aura symptoms 1
• Refer to neurology for genetic testing (PRRT2 gene accounts for majority of PKD cases) 1

Red Flags Requiring Urgent Evaluation

• Progressive weakness between episodes 2
• New neurologic deficits 2
• Signs of acute infection or cord compression 2
• Acute onset without prior similar episodes 2

Important Clinical Pitfalls

Do not dismiss these episodes as purely psychiatric without thorough neurological evaluation, as PKD is a genuine neurological disorder with genetic basis 1. However, maintain awareness that functional neurologic disorders can present similarly and require multidisciplinary assessment when organic causes are excluded 4, 5.

Fatigue alone does not explain episodic buckling—the combination of fatigue/stress as triggers with sudden movement-induced episodes is the key diagnostic pattern for PKD 1.