The left shoulder deltoid thickening acid consider deltoid muscle strain, bursitis, muscle strain, take medication or physical therapy. 1. deltoid strain: often do tired work or a fixed position for too long can cause chronic deltoid strain, localized pain, appropriate activities can be reduced, the application of muscle relaxation drugs such as ethopiridol or chlorzoxazone, local massage, the application of ultrashort wave physiotherapy. 2. Bursitis: aseptic inflammation of the bursa of the deltoid muscle, secretion of fluid will cause local thickening and acidity, you can take non-steroidal anti-inflammatory drugs such as diclofenac sodium enteric-coated tablets or ibuprofen extended-release tablets. Apply ultrasonic physiotherapy or infrared physiotherapy. 3. Muscle strain: due to trauma caused by local muscle fiber rupture, local tissue thickening, you can line cold compresses, external Yunnan Baiyao aerosol, deep red light treatment. The left deltoid muscle thickening acid if rest did not alleviate the timely to the hospital to check the cause and targeted treatment and processing.