Diagnostic Workup for Anhydrosis
The diagnostic workup for anhydrosis should include a comprehensive neurological evaluation, autonomic function testing, skin biopsy, and laboratory studies to identify the underlying cause, as anhydrosis can be associated with significant morbidity and mortality due to heat intolerance and potential heat stroke.
Initial Assessment
History
- Duration and pattern of anhydrosis (localized vs. generalized)
- Heat intolerance symptoms (flushing, dizziness, weakness, dyspnea)
- Associated symptoms (pain sensitivity, orthostatic symptoms)
- Family history (especially consanguinity)
- Medication review (anticholinergics, antidepressants)
- History of neurological disorders
- History of trauma or surgery
Physical Examination
- Vital signs including temperature
- Neurological examination with focus on:
- Sensory testing (pain, temperature)
- Motor function
- Deep tendon reflexes
- Autonomic function signs
- Skin examination for:
- Texture and moisture
- Evidence of self-injury (in cases of congenital insensitivity)
- Rashes or lesions
Diagnostic Testing
First-Line Tests
- Thermoregulatory sweat test (TST) - To document and quantify the distribution of anhydrosis
- Quantitative sudomotor axon reflex test (QSART) - To assess postganglionic sudomotor function
- Laboratory studies:
- Complete blood count
- Comprehensive metabolic panel
- Thyroid function tests
- Hemoglobin A1c (for diabetes)
- Serum protein electrophoresis (for amyloidosis)
Second-Line Tests
- Skin biopsy - To evaluate sweat gland morphology and innervation 1
- Autonomic function tests:
- Heart rate variability
- Blood pressure response to Valsalva maneuver
- Tilt table testing (if orthostatic symptoms present)
- Nerve conduction studies/EMG - To evaluate for peripheral neuropathy
Specialized Tests (Based on Clinical Suspicion)
- Sural nerve biopsy - May show absence of unmyelinated fibers in congenital cases 1
- Genetic testing - For suspected hereditary conditions like congenital insensitivity to pain with anhydrosis (CIPA) 2, 3
- Imaging studies:
- MRI brain/spine - If central nervous system pathology suspected
- Chest imaging - To rule out pulmonary or mediastinal pathology affecting sympathetic chain
Differential Diagnosis Categories
Congenital Causes
- Congenital insensitivity to pain with anhydrosis (CIPA) - characterized by absence of unmyelinated nerve fibers, self-mutilation, and insensitivity to pain and temperature 1, 2
Acquired Causes
- Chronic idiopathic anhydrosis - can be preganglionic or postganglionic 4, 5
- Medication-induced (anticholinergics, antidepressants)
- Neuropathic (diabetes, amyloidosis, Guillain-Barré syndrome)
- Central nervous system disorders (multiple system atrophy, Parkinson's disease)
- Skin disorders affecting sweat glands
Management Considerations
- Heat intolerance prevention strategies are critical as anhydrosis can lead to life-threatening heat stroke 5
- Patients with confirmed anhydrosis should be educated about:
- Avoiding excessive heat exposure
- External cooling methods
- Adequate hydration
- Recognition of early symptoms of heat-related illness
Follow-up
- Regular monitoring for progression of symptoms
- Assessment for development of other autonomic dysfunction
- Reevaluation if new neurological symptoms develop
- Long-term prognosis varies - some patients with chronic idiopathic anhydrosis may recover function while others may progress to generalized autonomic failure 4
Pitfalls and Caveats
- Anhydrosis may be overlooked as a cause of heat intolerance and heat stroke
- Patients with congenital forms may be unaware of their diagnosis, as seen in the case of a 43-year-old with CIPA who developed Charcot spine 3
- Failure to diagnose the underlying cause can lead to recurrent heat-related illness and potentially fatal outcomes
- Comprehensive evaluation is essential as anhydrosis may be the presenting symptom of a serious underlying neurological disorder