Author:
Editor(s):
Updated:
ULY CLINIC
ULY CLINIC
23 Septemba 2025, 12:37:35
Erb’s sign
Erb’s sign has two distinct clinical contexts:
Tetany (neuromuscular context): Increased irritability of motor nerves, which can be detected via electromyography (EMG). It reflects hyperexcitability of peripheral nerves, often associated with hypocalcemia or other electrolyte disturbances.
Acromegaly (cardiopulmonary context): Dullness on percussion over the manubrium of the sternum, indicating enlargement of the sternum or cardiac changes secondary to acromegaly.
Pathophysiology
Tetany-related Erb’s Sign
Hypocalcemia reduces the threshold for depolarization in peripheral motor nerves.
This leads to spontaneous or easily evoked action potentials, manifesting as muscle cramps or tetanic contractions.
EMG demonstrates increased nerve excitability in response to stimuli.
Acromegaly-related Erb’s Sign
Excess growth hormone leads to bony overgrowth and soft tissue thickening, including the sternum.
Percussion over the manubrium produces dullness instead of normal resonance due to structural changes in bone and underlying heart.
Examination Technique
Tetany Context
Place surface or needle EMG electrodes over the relevant muscles.
Apply electrical or mechanical stimulation to peripheral nerves.
Observe for exaggerated motor responses indicative of nerve hyperexcitability.
Acromegaly Context
Have the patient lie supine.
Percuss over the manubrium of the sternum.
A dull sound instead of normal resonance is considered a positive Erb’s sign.
Clinical Features
Context | Feature | Description |
Tetany | Motor nerve hyperexcitability | Muscle twitching, cramps, tetanic spasms detectable on EMG |
Acromegaly | Sternal dullness | Percussion over manubrium yields dull sound due to bony enlargement |
Differential Diagnosis
Cause / Condition | Key Features | Notes |
Hypocalcemia | Tetany, Chvostek and Trousseau signs, positive EMG | Often caused by hypoparathyroidism, vitamin D deficiency |
Electrolyte imbalance | Low magnesium, alkalosis | May exacerbate neuromuscular irritability |
Acromegaly | Enlarged hands/feet, prognathism, sternal dullness | Usually accompanied by cardiac and soft tissue changes |
Sternum pathology | Masses, infection, or trauma | Can also cause dull percussion; differentiate by imaging |
Pediatric considerations
Tetany-related Erb’s sign may be seen in infants with hypocalcemia, especially premature neonates.
EMG evaluation must be careful and minimally invasive.
Geriatric considerations
Acromegaly is rare in older adults, but long-standing GH excess may lead to detectable sternal changes.
Limitations
Tetany detection requires EMG, which may not be routinely available.
Percussion findings in acromegaly may be subtle and subjective; imaging may be more definitive.
Patient counseling
Explain that tetany-related Erb’s sign indicates nerve irritability, usually due to electrolyte imbalance.
Emphasize the importance of correcting underlying causes (e.g., calcium or vitamin D supplementation).
In acromegaly, explain that bony changes are secondary to hormone excess and require endocrine evaluation.
Conclusion
Erb’s sign is a dual-purpose clinical sign: in tetany, it reflects hyperexcitable motor nerves, and in acromegaly, it reflects sternal enlargement and dullness on percussion. Accurate recognition in either context can guide diagnosis and management of underlying electrolyte or endocrine disorders.
References
Erb W. Über Tetanie und ihre electrische Untersuchung. Dtsch Arch Klin Med. 1876;19:283–297.
Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 5th ed. New York: McGraw-Hill; 2013.
Ropper AH, Samuels MA, Klein JP. Adams and Victor’s Principles of Neurology. 11th ed. New York: McGraw-Hill; 2021.
Melmed S. Acromegaly: Pathogenesis and Clinical Features. N Engl J Med. 2006;355:2558–2573.