Final answer:
June's symptoms suggest that the initial diagnosis is likely Musculoskeletal strain, which matches her presentation of lower back pain, pain localized to muscles, muscle spasms, and relief with rest.
Step-by-step explanation:
Based on the description of June, a 59-year-old cashier presenting with lower back pain without sciatica, aggravated by sitting and certain movements, and alleviated with rest, an initial diagnosis would likely be B. Musculoskeletal strain. This condition is consistent with the symptoms of localized pain and muscle spasms, and the insidious onset with progressive improvement. The absence of sciatica rules out a herniated disc since sciatica is a common symptom of disc herniation, which often results in pain that radiates from the lower back down the thigh and into the leg.