Anhidrosis refers to the complete or partial absence of sweating, which may impair the body's ability to regulate temperature. It is categorized as:

• Generalized Anhidrosis: Involves the majority of the body’s surface. It poses a significant risk for hyperthermia and may be life-threatening.

• Localized Anhidrosis: Affects only a specific region of the body. Thermoregulation is typically preserved due to the limited area of sweat gland involvement.

Pathophysiology

Sweating is controlled by the autonomic nervous system via cholinergic sympathetic fibers that stimulate eccrine glands. Anhidrosis may result from:

1. Neurologic dysfunction:

   • Disruption in the sympathetic pathways (central or peripheral).

   • Disorders affecting the hypothalamus, spinal cord, or peripheral nerves.

2. Glandular dysfunction:

   • Congenital absence or acquired atrophy of eccrine glands.

   • Obstruction or destruction of sweat ducts (e.g., burns, skin diseases).

3. Pharmacologic interference:

   • Anticholinergic agents block muscarinic receptors, inhibiting sweat production.

Despite intact neurological signaling, absence or malfunction of sweat glands leads to failure of sweat production at the skin surface.

Clinical Presentation

Generalized Anhidrosis

• Patients may not be aware until exposed to heat or exertion.

• Presents with:

  • Hot, dry, flushed skin

  • Fatigue, dizziness, palpitations

  • Inability to tolerate heat

  • Risk of heat exhaustion or heatstroke

Localized Anhidrosis

Often identified incidentally or via:

• Compensatory hyperhidrosis in unaffected regions

• Localized skin dryness or scaling

• Chief complaint may be excess sweating in compensatory areas

Emergency Evaluation: Suspected Heatstroke

Key signs of life-threatening anhidrotic asthenia (heatstroke):

• Skin: Hot, dry, flushed

• Core temperature: > 102.2°F (39°C)

• CNS: Confusion, seizures, altered LOC

• CVS: Tachycardia, hypotension

• Other: Nausea, vomiting, muscle cramps, substernal tightness

Immediate Interventions

1. Measure rectal temperature (gold standard for core temp).

2. Check vital signs and LOC frequently.

3. Rapid cooling measures:

   • Ice water immersion

   • Evaporative cooling (cool mist + fan)

   • Cold IV fluids

4. Supportive care:

   • Oxygen supplementation if needed

   • Monitor urine output and electrolytes

   • Avoid antipyretics (ineffective in heatstroke)

History and Physical Examination

History

• Sweating pattern: Normal vs. diminished, profuse vs. absent

• Onset: Sudden or gradual

• Environmental exposure: Heat, physical activity

• Associated symptoms: Fever, weakness, heat intolerance

• Medical history:

  • Neurological diseases (e.g., diabetes, Parkinsonism)

  • Dermatologic disorders (e.g., psoriasis, ichthyosis)

  • Autoimmune conditions (e.g., scleroderma)

• Medication review: Especially anticholinergics, antidepressants, antipsychotics

Physical Examination

• Skin: Inspect for texture, dryness, scaling, or lesions

• Lesions: Document morphology, size, pattern, distribution

• Neurologic exam:

  • Sensory and motor deficits

  • Autonomic signs: orthostatic hypotension, urinary retention

Medical causes of anhidrosis

Other Causes

Diagnostic Investigations

When diagnosis is unclear, consider specialized testing:

1. Thermoregulatory Sweat Testing (TST):

   • Uses a color-changing powder or indicator (iodine-starch test)

   • Detects sweat distribution under controlled heat exposure

2. Quantitative Sudomotor Axon Reflex Test (QSART):

   • Assesses postganglionic sympathetic function by stimulating sweat via acetylcholine

3. Acetylcholine Sweat Stimulation Test:

   • Systemic cholinergic agents (e.g., pilocarpine) to induce sweating

4. Skin biopsy:

   • Evaluates sweat gland structure in cases of suspected congenital or acquired gland absence

Management

General Approach

• Treat underlying cause (neuropathy, dermatologic condition, medication withdrawal)

• Prevent heat-related complications

Patient Counseling

• Maintain cool environment

• Avoid strenuous activity and hot weather

• Use air conditioning, fans, light clothing

• Hydrate well, especially during warm weather

• Avoid spicy foods and alcohol

Medication Review

• Discontinue or replace offending drugs when possible

• Monitor for resolution or improvement in sweating

Special Populations

Pediatric considerations

• Common causes:

  • Congenital ectodermal dysplasia

  • Ichthyosis

  • Miliaria rubra (prickly heat)

• Premature infants: Delayed maturation of sweat glands can lead to transient anhidrosis

• Parental guidance: Avoid overdressing, monitor for signs of overheating

Summary

Anhidrosis, whether localized or generalized, demands a detailed clinical assessment due to its potential to impair thermoregulation and signal underlying systemic or neurologic disease. Generalized forms require urgent intervention, particularly in heatstroke scenarios. Diagnosis relies on history, physical exam, and targeted autonomic testing. Management includes treatment of underlying causes, supportive care, and patient education to prevent heat-related morbidity and mortality.

References

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