Which laboratory finding supports a myopathy over a neuropathy when evaluating weakness?

Which laboratory finding supports a myopathy over a neuropathy when evaluating weakness?

• A. Elevated CK levels.
• B. Decreased reflexes and sensory loss.
• C. Wasting with fasciculations.
• D. Asymmetric distal weakness.

Answer: (A)

Elevated CK levels indicate direct muscle injury. CK is an enzyme abundant in skeletal muscle, and when muscle fibers are damaged—as in inflammatory, dystrophic, or metabolic myopathies—CK leaks into the bloodstream, raising its level. In contrast, neuropathic weakness stems from nerve or motor-unit problems and typically does not cause a rise in CK unless there is secondary muscle damage, so CK tends to stay normal in pure neuropathies. The other clues you’d expect with nerve problems—decreased reflexes and sensory loss, wasting with fasciculations, or asymmetric distal weakness—point away from a primary muscle disorder. So, a laboratory finding of elevated CK best supports a myopathy over a neuropathy.

Elevated CK levels indicate direct muscle injury. CK is an enzyme abundant in skeletal muscle, and when muscle fibers are damaged—as in inflammatory, dystrophic, or metabolic myopathies—CK leaks into the bloodstream, raising its level. In contrast, neuropathic weakness stems from nerve or motor-unit problems and typically does not cause a rise in CK unless there is secondary muscle damage, so CK tends to stay normal in pure neuropathies. The other clues you’d expect with nerve problems—decreased reflexes and sensory loss, wasting with fasciculations, or asymmetric distal weakness—point away from a primary muscle disorder. So, a laboratory finding of elevated CK best supports a myopathy over a neuropathy.