What causes unilateral V1 hyperhidrosis?

Unilateral V1 Hyperhidrosis: Causes

Unilateral hyperhidrosis affecting the V1 (ophthalmic) distribution of the trigeminal nerve is almost always caused by central nervous system pathology, most commonly brainstem lesions, strokes, or tumors producing mass effect on autonomic pathways. 1

Primary Neurological Causes

The most important etiologies to consider for unilateral V1 hyperhidrosis include:

• Brainstem lesions with mass effect: Meningiomas or other tumors compressing brainstem autonomic centers can produce isolated unilateral sweating patterns, including facial distribution 1

• Cerebrovascular accidents: Brainstem or cerebral strokes affecting sympathetic pathways are well-documented causes of unilateral hyperhidrosis 1

• Hypothalamic lesions: Direct damage to hypothalamic autonomic centers can produce hemibody or focal unilateral sweating patterns 1

• Head trauma: Traumatic injury affecting central autonomic pathways may result in unilateral sweating abnormalities 1

Infectious Etiologies

Varicella zoster virus (VZV) reactivation affecting autonomic ganglia represents a rare but important infectious cause:

• VZV can damage the autonomic nervous system by reactivating in autonomic ganglia, producing unilateral sweating reduction or asymmetry 2

• This typically presents with herpes lesions in the affected dermatome, though autonomic symptoms may precede or follow the rash 2

• Diagnosis requires lumbar puncture showing VZV in cerebrospinal fluid and electromyographic skin sympathetic reflex testing demonstrating autonomic nerve damage 2

Critical Diagnostic Pitfalls

Do not assume bilateral symmetric disease: Unlike primary hyperhidrosis, which is always bilaterally symmetric and focal 3, unilateral patterns mandate neurological investigation 1, 4

Measure sweating rates systematically: Patients may have subclinical asymmetry in other body regions (arms, legs) that was not clinically apparent, suggesting more widespread autonomic dysfunction 4

Obtain urgent neuroimaging: Brain MRI with contrast is essential to exclude structural lesions, particularly in the brainstem and hypothalamus 1, 2

Diagnostic Algorithm

1. Confirm true unilateral pattern: Perform quantitative sweat testing (evaporative water loss measurements) on face, arms, and legs to document asymmetry 4

2. Obtain brain MRI with contrast immediately: Focus on brainstem, hypothalamus, and autonomic pathways to identify tumors, strokes, or demyelinating lesions 1, 2

3. Assess for infectious causes: If herpes lesions present or suspected, perform lumbar puncture for VZV PCR and consider electromyographic skin sympathetic reflex testing 2

4. Evaluate for trauma history: Document any prior head injury that could have damaged central autonomic centers 1

The key distinction is that unilateral hyperhidrosis is secondary (caused by underlying pathology) rather than primary, and neurological causes predominate. 1, 4 This contrasts sharply with typical primary hyperhidrosis, which is bilateral, symmetric, and has no identifiable underlying cause 3, 5.