Differential Diagnosis for One-Sided Tender Neck Muscles

Single Most Likely Diagnosis

• Muscle Strain: This is the most common cause of neck pain and tender neck muscles, often resulting from overuse, poor posture, or direct injury to the muscle. The fact that the pain is one-sided and has persisted for over a month could indicate a chronic strain or an ongoing activity that continues to irritate the muscle.

Other Likely Diagnoses

• Cervical Spondylosis: This condition involves wear and tear on the disks in the neck, which can cause pain and stiffness, especially on one side if the degeneration is asymmetric. It's common in older adults and can lead to chronic neck pain.
• Torticollis: A condition characterized by a twisted neck, where the head becomes persistently turned to one side. It can cause one-sided neck muscle tenderness due to the spasms and strain on the muscles.
• Referred Pain from the Shoulder: Sometimes, pain from the shoulder can be referred to the neck, especially if there's an issue like a rotator cuff injury or shoulder bursitis. This could cause one-sided tender neck muscles if the shoulder condition is on one side.

Do Not Miss Diagnoses

• Cervical Herniated Disk: Although less common, a herniated disk in the neck can cause significant pain and muscle tenderness on one side, especially if it's compressing a nerve root. Missing this diagnosis could lead to prolonged pain and potential neurological deficits.
• Meningitis: Inflammation of the protective membranes covering the brain and spinal cord, which can cause severe neck pain and stiffness, often accompanied by fever, headache, and vomiting. It's a medical emergency.
• Cancer: Although rare, cancers such as lymphoma or metastatic disease to the cervical spine or soft tissues can cause persistent one-sided neck pain and muscle tenderness.

Rare Diagnoses

• Polymyalgia Rheumatica (PMR): An inflammatory condition that causes widespread muscle pain and stiffness, particularly in the neck, shoulders, and hips. It's more common in older adults and can cause one-sided symptoms, although it typically affects both sides.
• Fibromyalgia: A chronic condition characterized by widespread muscle pain, fatigue, and tender points. While it's not typically one-sided, some patients may experience more pronounced symptoms on one side of the body.
• Temporal Arteritis: Inflammation of the blood vessels in the head, which can cause pain in the neck and jaw, especially when chewing. It's rare and usually affects older adults.