THE CLINICAL SYNDROME
In contradistinction to most other causes of pain involving the chest wall that are musculoskeletal in nature, the pain of intercostal neuralgia is neuropathic. As with costosternal joint pain, Tietze’s syndrome, and rib fractures, a significant number of patients who suffer from intercostal neuralgia first seek medical attention because they believe they are suffering a heart attack. If the subcostal nerve is involved, patients may believe they are suffering from gallbladder disease. The pain of intercostal neuralgia is due to damage or inflammation of the intercostal nerves. The pain is constant and burning in nature and may involve any of the intercostal nerves as well as the subcostal nerve of the twelfth rib. The pain usually begins at the posterior axillary line and radiates anteriorly into the distribution of the affected intercostal or subcostal nerves, or both.
The pain of intercostal neuropathic rather than musculoskeletal in origin.
Deep inspiration or movement of the chest wall may slightly increase the pain of intercostal neuralgia, but to a much lesser extent compared with the pain associated with the musculoskeletal causes of chest wall pain, such as costosternal joint pain, Tietze’s syndrome, and broken ribs.
SIGNS AND SYMPTOMS
Physical examination of the patient suffering from intercostal neuralgia will generally reveal minimal physical findings unless there is a history of previous thoracic or subcostal surgery or cutaneous findings of herpes zoster involving the thoracic dermatomes. In contradistinction to the aforementioned musculoskeletal causes the chest wall and subcostal pain, the patient suffering from intercostal neuralgia does not attempt to splint or protect the affected area. Careful sensory examination of the affected dermatomes may reveal decreased sensation or allodynia. With significant motor involvement of the subcostal nerve, the patient may complain that his or her abdomen bulges out.
Initial treatment of intercostal neuralgia should include a combination of simple analgesics and the nonsteroidal anti-inflammatory drugs or the cyclooxygenase-2 inhibitors. If these medications do not adequately control the patient’s symptomatology, a tricyclic antidepressant or gabepentin should be added.
Traditionally, the tricyclic antidepressants have been a mainstay in the palliation of pain secondary to intercostal neuralgia. Controlled studies have demonstrated the efficacy or amitriptyline for this indication. Other tricyclic antidepressants, including nortriptyline and desipramine, have also shown to be clinically useful. Unfortunately, this class of drugs is associated with significant anticholinergic side effects, including dry mouth, constipation, sedation, and urinary retention.
If the antidepressant compounds are ineffective or contraindicated, gabapentin represents a reasonable alternative. Gabapentin should be started with a 300-mg dose at bedtime for 2 nights. The drug is then increased in 300-mg increments, given in equally divided doses over 2 days, as side effects allow until pain relief is obtained or a total dosage of 2400 mg daily is reached.
The local application of heat and cold may also be beneficial to provide symptomatic relief of the pain of intercostal neuralgia. The use of an elastic rib belt may also help provides symptomatic relief. For patients who do not respond to these treatment modalities, the following injection technique using local anesthetic and steroid may be a reasonable next step.
The patient is placed in the prone position with the patient’s arm hanging loosely off the side of the cart. Alternatively, this block can be done with the patient in the sitting or lateral position. The rib to be blocked is identified by palpating its path at the posterior axillary line. Subsequent daily nerve blocks are carried out in a similar manner, substituting 40 mg methylprednisolone for the initial 80-mg dose. Because of the overlapping innervation of the chest and upper abdominal wall, the intercostal nerves above and below the nerve suspected of subserving the painful condition will have to be blocked.