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What is the differential diagnosis in a patient with anterior thigh pain, persistently elevated CK, positive rheumatoid factor, positive RNA with speckled pattern, and an abnormal but not diagnostic muscle biopsy, including electron microscopy?

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Image - Photo of Lawrence J. Kagen, MD - Emeritus
Lawrence J. Kagen, MD - Emeritus
Physician Emeritus, Hospital for Special Surgery

Thigh pain can arise at the location where it is perceived, or it may be referred from elsewhere. Most referred thigh pain originates from nerve roots in the lumbar spine or possibly from the femoral cutaneous nerve. An electromyogram would be helpful in determining whether pain is of neurogenic origin.

Muscle is the next possible source of thigh pain. In a patient who has an elevated creatine kinase level and a biopsy reported as abnormal but not diagnostic, abnormalities should be sought elsewhere to determine if there is any evidence of generalized myopathy. This would include an evaluation for muscle weakness and a magnetic resonance imaging study of the thigh. It is possible that the biopsy might have missed important elements due to sampling error. Sonography can also be used to evaluate muscle tissue.

The MRI will also be of value in assessing the femoral bone structure as well as the hip joint.

It is also of importance to evaluate the patient's endocrinological status. Hypothyroidism can cause muscle pain.

Medications, also, such as the statins, may cause myalgia.

Further assessment, as suggested, should help you to come to a more precise diagnosis of the cause of pain.


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