Final answer:
Elevated blood sugar levels are a potential systemic complication of corticosteroid injections due to the role of cortisol in glucose metabolism and its similarity to the effects of Cushing's syndrome.
Step-by-step explanation:
The potential systemic complication of corticosteroid injection is C) Elevated blood sugar levels. Corticosteroids, such as cortisol and synthetic alternatives, can induce hyperglycemia as a side effect. This is because cortisol plays a pivotal role in the regulation of glucose metabolism, including stimulating gluconeogenesis, which raises blood glucose levels. Systemic absorption of injected corticosteroids can mimic the effects of endogenous cortisol overproduction, as seen in Cushing's syndrome, which is characterized by high blood glucose levels and other metabolic disturbances.