Muscle strain or overuse: This is a common condition that can lead to mild creatine kinase elevation due to muscle damage. The normal CT head suggests that there is no significant intracranial pathology, making this a plausible explanation for the symptoms.

Rhabdomyolysis (mild): Although the creatine kinase elevation is mild, rhabdomyolysis should be considered, especially if there are other symptoms such as muscle weakness or dark urine.
Viral myositis: Certain viral infections can cause muscle inflammation, leading to elevated creatine kinase levels.
Medication-induced myopathy: Some medications, such as statins, can cause muscle damage and elevate creatine kinase levels.

Acute coronary syndrome: Although the CT head is normal, cardiac causes of chest pain or muscle damage should not be overlooked, as acute coronary syndrome can be life-threatening.
Pulmonary embolism: This is another potentially life-threatening condition that may not be directly related to the CT head or creatine kinase elevation but should be considered in the differential diagnosis.
Trauma: Even if the CT head is normal, trauma to other parts of the body could cause muscle damage and elevate creatine kinase levels.

Dermatomyositis or polymyositis: These are autoimmune conditions that can cause muscle inflammation and damage, leading to elevated creatine kinase levels.
Mitochondrial myopathies: These are a group of rare genetic disorders that affect the mitochondria and can cause muscle weakness and elevated creatine kinase levels.
Glycogen storage diseases: Certain genetic disorders that affect glycogen metabolism can cause muscle damage and elevate creatine kinase levels.