Masquerade: Nonspinal musculoskeletal disorders that mimic spinal conditions
ABSTRACTNonspinal musculoskeletal disorders frequently cause neck and back pain and thus can mimic conditions of the spine. Common mimics are rotator cuff tears, bursitis in the hip, peripheral nerve compression, and arthritis in the shoulder and hip. A thorough history and physical examination, imaging studies, and ancillary testing can usually help determine the source of pain.
KEY POINTS
- Neck pain is commonly caused by shoulder problems such as rotator cuff disease, glenohumeral arthritis, and humeral head osteonecrosis.
- Brachial neuritis involves acute, severe neck or shoulder pain, followed by weakness as pain resolves.
- Low back pain can be caused by hip or spine arthritis, femoral head osteonecrosis, an occult or impending femoral neck fracture, hip dysplasia, piriformis syndrome, and bursitis.
- Bony and soft tissue masses can be detected with imaging studies.
- Peripheral nerve compression can mimic cervical or lumbar spine radiculopathy. Electromyography and eliciting symptoms by tapping over the compressed nerve aid in making a diagnosis.
- Patients with human immunodeficiency virus infection, alcoholism, or corticosteroid use are at increased risk of developing osteonecrosis of the humeral or femoral head.
Femoral necrosis or fractures are detectable by imaging
Femoral head osteonecrosis is another intra-articular hip process that can cause backpain.13 As is also true of osteonecrosis of the shoulder, patients who abuse alcohol or take corticosteroids are at increased risk. Recently, human immunodeficiency virus has also been associated with this condition.
Femoral head osteonecrosis typically presents with insidiously worsening reduction of hip rotation and pain in the buttock, thigh, and groin. The pain is not in a dermatomal pattern and is usually unilateral but can be bilateral.18
Radiographs can be diagnostic for femoral head collapse in late disease. MRI is best for diagnosing early disease before collapse occurs.
Occult or impending femoral neck fracture (ie, in metastatic or metabolic bone disease) usually presents with groin pain, similar to hip osteoarthritis and osteonecrosis,13 but it can also present with vague back pain with or without groin pain. The pain is produced by weight-bearing on the affected leg. Young patients with femoral neck stress fractures or primary benign bone lesions of the hip can also present with buttock pain that can be misinterpreted as coming from the back.
MRI of the pelvis and proximal femur is best for diagnosing a stress fracture and some bone lesions, because they are often not visible on radiographs.
Because the rate of osteonecrosis is very high in displaced femoral neck fractures, it is important that an impending fracture be detected and treated before a complete fracture occurs.
Hip dysplasia requires early treatment
Hip dysplasia, in which the hip joint does not develop normally, can present as back, buttock, and groin pain in young patients. Back pain may be caused by asymmetric spinal loading and abnormal muscular tension in the lumbar spine.13 Early diagnosis is important so that it can be surgically treated (with osteotomies of the proximal femur or pelvis, or both) to preserve hip function.
Piriformis syndrome occurs in athletic patients
Piriformis syndrome, which mimics sciatica from a spinal cause, is controversial because the diagnosis must be based on history and clinical findings without any objective imaging or electrodiagnostic testing. The condition is thought to be caused by sciatic nerve entrapment and compression under the piriformis muscle, which externally rotates the hip and may become swollen and inflamed inactive, athletic people.13,16
The diagnosis is confirmed on physical examination if the pain is replicated when the piriformis muscle is stretched by externally rotating the hip (ie, with the patient supine, flexing the affected hip and knee and pulling the ipsilateral knee toward the contralateral shoulder).13,16
Imaging studies of the spine or hip are notd iagnostic but should be done to look for other possible causes of the pain.
Some patients with this condition are helped by exercises to stretch the hip muscles, particularly the external rotators.
Bursitis causes localized tenderness
Trochanteric bursitis is a fairly common soft-tissue problem that can cause pain along the lateral aspect of the hip and proximal thigh. Unlike radiculopathy, the condition causes localized tenderness over the greater trochanter.
Ischial bursitis can cause back pain and can be differentiated from spinal pathology by localized tenderness over the ischial tuberosity.
Peripheral nerve compression can cause radicular pain
Peripheral nerve compression in and around the leg can cause radicular pain that mimics lumbar spine pathology.
The lateral femoral cutaneous nerve, if compressed and irritated as it exits the pelvis, can cause meralgia paresthetica, which is characterized by pain, numbness, and tinglingin the anterolateral proximal thigh, mimicking an L1 or L2 radiculopathy. Many patients report that the pain worsens when they wear a belt or tight pants and improves when they remove or loosen them.
The saphenous and peroneal nerves can be compressed around the knee, causing paresthesias in the medial and lateral aspect of the knee and leg, respectively, mimicking a radiculopathy of the nerve roots at L3-L4 (saphenous nerve) and L5 (peroneal nerve).
The tibial nerve can be compressed in the tarsal tunnel on the medial aspect of the ankle, causing distal paresthesias in the medial aspect of the foot, mimicking radiculopathy at L4-L5.
Stimulating the area of nerve compression by external compression or tapping with the examiner’s fingers generally causes paresthesias and aggravates the symptoms. Electromyography can also help with diagnosis.
