Final answer:
Evelyn's symptoms suggest a musculoskeletal disorder as her initial diagnosis, which includes lower back pain that improves with rest and is aggravated by certain postures and movements.
Step-by-step explanation:
Evelyn, a 59-year-old cashier, is presenting with lower back pain without a precipitating event. Given the absence of sciatica and the localization of pain and muscle spasms upon palpation, her initial diagnosis may incline towards musculoskeletal disorder, such as a strain or sprain, or potentially the beginning stages of a degenerative condition like osteoarthritis, particularly considering her age and occupational hazards. With an insidious onset of pain that improves with rest and is aggravated by sitting, standing, and movements, it's less likely to be a nerve compression disorder like herniated disc unless further investigation reveals additional symptoms. It's important for Evelyn to seek a medical evaluation for proper diagnostic imaging and testing to confirm the diagnosis and begin appropriate treatment.