What causes paresthesia in the head, face, and back?

Paresthesia of the Head, Face, and Back: Causes and Diagnostic Approach

Primary Etiologic Categories

Paresthesias in the head, face, and back result from either central nervous system pathology (brainstem ischemia, structural lesions, inflammation) or peripheral nervous system disorders (cranial neuropathies, nerve entrapment, metabolic disturbances), with the specific distribution pattern guiding diagnostic evaluation. 1

Central Nervous System Causes

Central pathology affecting the brainstem or cortex can produce facial paresthesias through several mechanisms:

• Ischemic events including brainstem infarction can cause isolated facial sensory symptoms, though typically accompanied by other neurologic deficits 2
• Structural lesions such as tumors, vascular malformations, or multiple sclerosis affecting the pons or medulla may produce facial numbness 2
• Inflammatory conditions including demyelinating disease can affect sensory pathways in the brainstem 2

Peripheral Nervous System Causes

Trigeminal Nerve (CN V) Pathology

The trigeminal nerve provides most sensation to the face, and its dysfunction is a common cause of facial paresthesias:

• Trigeminal sensory neuropathy can result from local trauma, iatrogenic injury, systemic diseases, or rarely hereditary conditions like hereditary neuropathy with liability to pressure palsies 3
• Trigeminal neuralgia typically presents with severe, stabbing pain rather than pure paresthesias, but sensory symptoms may occur 2
• Nerve compression from tumors (schwannomas, meningiomas), vascular lesions, or inflammatory processes along the nerve's course can produce numbness 2

Facial Nerve (CN VII) Involvement

While primarily a motor nerve, CN VII carries sensory fibers that can produce paresthesias:

• Bell's palsy may present with facial pain or paresthesias in addition to weakness, affecting taste sensation to the anterior two-thirds of the tongue 4
• Inflammatory processes affecting the facial nerve within the temporal bone can cause sensory symptoms 2

Cervical Nerve Root Pathology

Paresthesias radiating to the back of the head suggest upper cervical nerve involvement:

• Upper cervical nerves (C2-C3) provide innervation to the posterior scalp and neck, with compression or inflammation causing radiating paresthesias 5
• Cervical radiculopathy from disc herniation, spondylosis, or foraminal stenosis can produce symptoms extending from the neck to the occiput 1

Metabolic and Systemic Causes

• Diabetes mellitus is the most common cause of peripheral neuropathy, though typically affects distal extremities before cranial nerves 6
• Vitamin B12 deficiency can produce paresthesias in various distributions including facial regions 6
• Monoclonal gammopathy and other hematologic disorders may cause sensory neuropathy 6

Critical Diagnostic Red Flags

Multiple cranial nerve involvement mandates immediate MRI regardless of symptom duration, as this suggests serious structural pathology rather than isolated neuropathy. 7, 8

Urgent Evaluation Required For:

• Acute onset (within days) with rapid progression suggests vascular events or Guillain-Barré syndrome 6, 1
• Associated motor weakness, diplopia, dysphagia, or dysarthria indicates brainstem pathology requiring emergent imaging 7
• Bilateral symptoms are extremely rare in benign conditions and suggest systemic disease, Guillain-Barré syndrome, or bilateral structural lesions 4
• Severe dysautonomia accompanying paresthesias may indicate serious peripheral or autonomic neuropathy 6

Diagnostic Algorithm

Initial Clinical Assessment

1. Determine distribution pattern:

   • Pure facial involvement suggests trigeminal nerve pathology 3
   • Facial plus posterior head/neck suggests combined trigeminal and upper cervical nerve involvement 5
   • Multiple cranial nerve territories indicate brainstem or skull base pathology 8

2. Assess for motor involvement:

   • Facial weakness with forehead involvement indicates peripheral CN VII lesion 7, 4
   • Forehead sparing suggests central (stroke) pathology 7
   • Tongue deviation with facial symptoms localizes to skull base or lower brainstem 8

3. Evaluate temporal pattern:

   • Transient, ultrashort stabs suggest primary stabbing headache rather than neuropathy 9
   • Progressive symptoms over weeks to months suggest compressive or inflammatory etiology 2
   • Acute onset with other neurologic signs requires stroke evaluation 7

Imaging Strategy

MRI with and without contrast is the preferred imaging modality for evaluating facial and cranial paresthesias, as it directly visualizes the entire course of cranial nerves from brainstem through skull base to extracranial segments. 2, 8

MRI Indications:

• Immediate MRI required for multiple cranial nerve involvement, associated motor deficits, or progressive symptoms 7, 8
• MRI within 2-4 months for isolated facial paresthesias persisting beyond typical Bell's palsy recovery period 2, 4
• MRI sequences should include thin-section imaging through the brainstem, skull base, and temporal bones with gadolinium contrast 2

CT Temporal Bone Role:

• High-resolution CT provides complementary information for osseous pathology, temporal bone fractures, and foraminal expansion 2
• CT is insufficient alone for evaluating cranial neuropathies but useful when MRI contraindicated or for surgical planning 2

Laboratory Evaluation

Targeted laboratory testing based on clinical suspicion:

• Diabetes screening (hemoglobin A1c, fasting glucose) for patients with risk factors 6
• Vitamin B12 level particularly in elderly patients or those with dietary restrictions 6
• Lyme serology in endemic areas or with appropriate exposure history 8, 4
• Serum protein electrophoresis if monoclonal gammopathy suspected 6

Common Pitfalls to Avoid

• Do not assume isolated facial paresthesias are benign without excluding structural causes, especially if symptoms persist beyond 2-4 months 2, 4
• Do not overlook subtle motor findings that may indicate more serious pathology than pure sensory symptoms suggest 7
• Do not attribute bilateral facial symptoms to Bell's palsy, as this is extremely rare and warrants investigation for systemic disease 4
• Do not rely on CT head alone for cranial neuropathy evaluation, as it inadequately visualizes nerve pathways and soft tissue lesions 2
• Do not delay imaging when multiple cranial nerves are involved, as this pattern suggests skull base or brainstem pathology requiring urgent diagnosis 7, 8