What are the potential causes of lateral leg numbness in a 15-year-old female yoga practitioner without a reported acute physical injury?

Differential Diagnoses for Lateral Leg Numbness in a 15-Year-Old Female Yoga Practitioner

The most likely diagnosis in this adolescent yoga practitioner is common peroneal (fibular) nerve compression at the fibular head from prolonged cross-legged sitting positions, though meralgia paresthetica and lumbar radiculopathy must also be considered based on the specific distribution of symptoms.

Primary Differential Diagnoses

Common Peroneal Nerve Compression

• The common peroneal nerve is particularly vulnerable to compression as it wraps around the fibular head, making it susceptible to injury from prolonged cross-legged sitting positions commonly used in yoga practice 1
• Presents with numbness and paresthesias over the lateral leg and dorsum of the foot, which matches the "lateral leg" description 1
• This is the most common lower extremity compression neuropathy after sciatic nerve injury and frequently occurs without acute trauma 1
• Yoga practitioners are at increased risk due to sustained pressure during seated meditation poses (lotus position, cross-legged sitting) 1

Meralgia Paresthetica (Lateral Femoral Cutaneous Nerve Entrapment)

• Characterized by numbness and paresthesias on the anterolateral aspect of the thigh without motor deficits 2, 3
• Can occur from prolonged positioning or tight clothing around the inguinal ligament region 2, 4
• Tinel's sign may be positive over the lateral femoral cutaneous nerve in the inguinal ligament region 2
• This diagnosis is more likely if the numbness is confined to the thigh rather than extending below the knee 2, 3

L5 Radiculopathy

• L5 nerve root compression causes sensory loss in the dorsal aspect of the foot and lateral leg, which could present as "lateral leg numbness" 5
• Typically associated with L5-S1 disc pathology, though this can occur without acute injury in adolescents 1, 5
• MRI is the mainstay of imaging for lumbosacral nerve root pathology if this diagnosis is suspected 1, 5
• Clinical diagnosis should be confirmed by electrodiagnostic studies 5

Lumbar Plexopathy

• The lumbar plexus (L1-L5) can cause lateral leg symptoms when affected 1
• Plexopathy manifests as pain with neuropathic character, dysesthesia, or burning sensation occurring in more than one peripheral nerve distribution 1
• Less likely in a young, healthy yoga practitioner without trauma, but must be considered if symptoms involve multiple nerve distributions 1

Critical Clinical Distinctions

Anatomical Localization

• If numbness is isolated to the anterolateral thigh: Consider meralgia paresthetica first 2, 3
• If numbness involves the lateral leg below the knee and dorsum of foot: Consider common peroneal nerve compression or L5 radiculopathy 1, 5
• If numbness includes the big toe and dorsal foot: L5 radiculopathy becomes more likely 5

Associated Findings to Assess

• Motor weakness in foot dorsiflexion or great toe extension suggests L5 radiculopathy rather than pure sensory neuropathy 5
• Absence of motor deficits favors meralgia paresthetica or pure sensory nerve compression 2, 3
• Tinel's sign at the fibular head supports common peroneal nerve compression 1
• Tinel's sign at the inguinal ligament supports meralgia paresthetica 2

Less Likely but Important Considerations

Peripheral Artery Disease (PAD)

• Extremely unlikely in a 15-year-old without significant risk factors 1
• PAD typically presents with exertional leg symptoms including tingling, numbness, or burning that occur during walking and resolve with rest 1
• This diagnosis should only be considered if symptoms are clearly exercise-induced and relieved by rest, with associated risk factors 1

Vascular Causes

• Ipsilateral leg numbness from vascular insufficiency is rare and typically associated with other neurological signs 6
• Not a primary consideration in a healthy adolescent yoga practitioner 6

Diagnostic Approach

Initial Clinical Assessment

• Precise mapping of the sensory distribution is essential to differentiate between nerve territories 1
• Assess for motor weakness, particularly foot dorsiflexion and great toe extension 5
• Examine for Tinel's sign at the fibular head and inguinal ligament 1, 2
• Evaluate ankle reflexes (affected in S1 radiculopathy, not L5) 5

Imaging Considerations

• MRI is the mainstay for evaluating plexopathy or radiculopathy if clinical examination suggests nerve root involvement 1, 5
• MRI provides superior definition of intraneural anatomy and pathologic lesions 1
• Electrodiagnostic studies should confirm clinical diagnosis and differentiate radiculopathy from plexopathy 5
• Imaging is typically not needed for straightforward peripheral nerve compression syndromes that respond to conservative management 1, 2

Common Pitfalls

• Assuming all lateral leg numbness is L5 radiculopathy: Common peroneal nerve compression is actually more frequent and often overlooked 1
• Missing the yoga-specific risk factors: Prolonged cross-legged positions create sustained pressure on the common peroneal nerve 1
• Ordering premature imaging: Most peripheral nerve compression syndromes respond to activity modification and do not require imaging initially 1, 2
• Confusing nerve territories: The lateral femoral cutaneous nerve affects only the thigh, while the common peroneal nerve affects the lateral leg below the knee 1, 2