What is the cause of left-sided excessive sweating with increased temperature on the right side?

Unilateral Sweating with Contralateral Temperature Asymmetry

Left-sided excessive sweating (diaphoresis) with increased temperature on the right side most likely indicates a sympathetic nervous system dysfunction, specifically Harlequin syndrome or a related autonomic disorder where the non-sweating (right) side has an underlying sympathetic deficit at the second or third thoracic spinal segment level, causing the intact left side to compensate with excessive sweating and flushing.

Understanding the Mechanism

This presentation represents a compensatory hyperhidrosis where one side sweats excessively because the opposite side cannot respond normally. The key insight is counterintuitive: the side that appears "abnormal" with excessive sweating is actually functioning normally or hyperactively, while the seemingly normal side has the underlying pathology 1.

Pathophysiology

• The right side (with increased temperature but no sweating) has impaired thermal and emotional sweating/flushing due to sympathetic pathway disruption
• The left side compensates with excessive sweating when exposed to heat or exercise
• This typically indicates a lesion affecting the second sympathetic neuron at the T2-T3 spinal segment level 1

Differential Diagnosis by Pattern

1. Harlequin Syndrome (Most Likely)

• Sudden onset of unilateral facial flushing and sweating triggered by heat or vigorous exercise
• Thermal and emotional sweating impaired on the non-flushing side
• May occur without obvious Horner's syndrome signs 1
• Can result from anterior radicular artery occlusion at T3 during spinal torsion from strenuous activity 1

2. Cervical Disc Herniation with Myelopathy

• Lateral compression pattern: Well-demarcated hypohidrosis below hyperhidrosis on the same side as the cervical lesion
• Paramedian compression pattern: Poorly demarcated changes on the contralateral side 2
• Affects sudomotor pathway circulation or sympathetic descending pathway
• Requires cervical MRI evaluation 2

3. Central Nervous System Lesions

• Hypothalamic involvement can cause contralateral hyperhidrosis 3
• Brainstem infarction may present with subtle contralateral Horner's syndrome 1
• Consider in patients with acute neurological symptoms

Diagnostic Approach

Immediate Clinical Assessment

Look for these specific findings:

• Ocular signs: Check for subtle Horner's syndrome (ptosis, miosis, anhidrosis) on the right side
• Onset timing: Sudden onset after strenuous exercise suggests vascular etiology 1
• Trigger patterns: Heat or exercise-induced suggests Harlequin syndrome 1
• Distribution: Face, forehead, shoulder involvement indicates higher thoracic lesion 1, 2

Essential Diagnostic Tests

1. Sweat function testing and thermography - Confirms hyperhidrosis/hypohidrosis distribution and determines the focus 2
2. Cervical and upper thoracic MRI - Evaluate for:
   • Disc herniation at C5-T3 levels 2
   • Intraspinal lesions or signal abnormalities
   • Vascular malformations
3. Brain MRI with focus on hypothalamus and brainstem - If central etiology suspected 3

Additional Considerations

Rule out secondary causes:

• Thyroid function tests (hyperthyroidism can cause generalized sweating but not typically unilateral) 4
• Exclude panic disorders, sleep disorders if night sweats predominate 5
• Consider menopause in appropriate demographic 4

Clinical Pitfalls

⚠️ Common Mistakes to Avoid:

• Don't assume the sweating side is abnormal - The pathology is usually on the non-sweating side 1
• Don't miss subtle Horner's syndrome - Carefully examine pupils and eyelids on the right side
• Don't overlook recent vigorous exercise - This may precipitate vascular compromise at T3 level 1
• Don't investigate only one side - Sweat testing and imaging should evaluate both sides 2

Management Considerations

When Structural Lesion Identified

• Neurosurgical consultation for cervical disc herniation causing myelopathy 2
• Vascular neurology consultation for suspected ischemic events 1

When No Structural Lesion Found

• Stellate ganglionectomy on the sweating (left) side can abolish symptoms 1
• This is typically reserved for severely symptomatic cases
• Conservative management with trigger avoidance (heat, strenuous exercise) may be sufficient

Prognosis

The underlying sympathetic deficit is often permanent, but symptoms may stabilize. One patient in the literature had complete symptom resolution after ipsilateral stellate ganglionectomy 1.

The critical next step is obtaining sweat function testing with thermography to map the exact distribution of hyper- and hypohidrosis, followed by MRI of the cervical spine and upper thoracic region to identify the anatomical lesion causing the sympathetic pathway disruption.