Final answer:
To distinguish severe innervational or mechanical causes of upper arm issues, tests that differentiate between upper and lower motor neuron damage are conducted. These include evaluating muscle tone, strength against resistance, deep tendon reflexes, pronator drift, the Babinski sign, spasticity, and the clasp-knife response.
Step-by-step explanation:
To differentiate a severe innervational or mechanical cause of upper arm (UA) dysfunction, various tests assessing motor function can be conducted. These tests help in determining whether the damage is within the upper motor neurons (UMN) or lower motor neurons (LMN). If muscle tone is adequate, the physician may test muscle strength by having the patient resist applied pressure, for example, pushing down on an upwardly extended arm. Lateral differences in strength could indicate corticospinal tract deficits. Additionally, other signs of UMN lesions may be observed, such as strong deep tendon reflexes, pronator drift, a positive Babinski sign, spasticity, or the clasp-knife response. In contrast, LMN damage may present as hypotonicity or flaccidity, suggesting failure in neuromuscular signaling.