The Clinical Syndrome

Diabetic neuropathy is a term used by clinicians to describe a heterogeneous group of diseases that affect the autonomic and peripheral nervous systems of patients suffering from diabetes mellitus. Diabetic neuropathy is now thought to be the most common form of peripheral neuropathy that afflicts humankind, with an estimated 220 million people worldwide suffering from this malady.

One of the most commonly encountered forms of diabetic neuropathy is diabetic truncal neuropathy. In this condition, pain and motor dysfunction are often incorrectly attributed to intrathoracic or intraabdominal disorders and lead to extensive workups for appendicitis, cholecystitis, renal calculi, and so on. The onset of symptoms frequently coincides with periods of extreme hypoglycemia or hyperglycemia or with weight loss or gain. Patients who present with diabetic truncal neuropathy complain of severe dysesthetic pain with patchy sensory deficits in the distribution of the lower thoracic or upper thoracic dermatomes. The pain is often worse at night and causes significant sleep disturbance. The symptoms of diabetic truncal neuropathy often resolve spontaneously over 6 to 12 months. However, because of the severity of symptoms, aggressive treatment with pharmacotherapy and neural blockade is indicated.

Signs and Symptoms

Physical examination generally reveals minimal findings unless the patient has a history of previous thoracic or subcostal surgery or cutaneous evidence of herpes zoster involving the thoracic dermatomes. Unlike patients with musculoskeletal causes of chest wall and subcostal pain, patients with diabetic truncal neuropathy do 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 outward ( Fig. 64.1 ). This abnormal bulging is known as pseudohernia ( Fig. 64.2 ).

The pain of diabetic truncal neuropathy is neuropathic and is often made worse by poorly controlled blood glucose levels.

With significant motor involvement of the subcostal nerve, a patient suffering from diabetic truncal neuropathy may complain that his or her abdomen bulges outward.

Testing

The presence of diabetes should lead to a high index of suspicion for diabetic truncal neuropathy. If the diagnosis of diabetic truncal neuropathy is suspected based on the targeted history and physical examination, screening laboratory tests, including a complete blood count, chemistry profile, erythrocyte sedimentation rate, thyroid function studies, antinuclear antibody testing, and urinalysis, should rule out most other peripheral neuropathies that are easily treatable. Electromyography and nerve conduction velocity testing are indicated in all patients suffering from peripheral neuropathy, to identify treatable entrapment neuropathies and further delineate the type of peripheral neuropathy present; these tests may also be able to quantify the severity of peripheral or entrapment neuropathy. Additional laboratory testing is indicated as the clinical situation dictates (e.g., Lyme disease titers, heavy metal screens). Magnetic resonance imaging of the spinal canal and cord should be performed if myelopathy is suspected. Nerve or skin biopsy is occasionally indicated if no cause of the peripheral neuropathy can be ascertained. Lack of response to the therapies discussed later should lead to a reconsideration of the diagnosis and the repetition of testing, as clinically indicated.

Differential Diagnosis

Diseases other than diabetic neuropathy may cause peripheral neuropathies in diabetic patients. These diseases may exist alone or may coexist with diabetic truncal neuropathy, thus making identification and treatment difficult.

Although uncommon in the United States, Hansen’s disease is a common cause of peripheral neuropathy worldwide that may mimic or coexist with diabetic truncal neuropathy. Other infectious causes of peripheral neuropathies include Lyme disease and human immunodeficiency virus infection. Substances that are toxic to nerves, including alcohol, heavy metals, chemotherapeutic agents, and hydrocarbons, may also cause peripheral neuropathies that are indistinguishable from diabetic neuropathy on clinical grounds. Heritable disorders such as Charcot-Marie-Tooth disease and other familial diseases of the peripheral nervous system must also be considered, although treatment options are somewhat limited. Metabolic and endocrine causes of peripheral neuropathy that must be ruled out include vitamin deficiencies, pernicious anemia, hypothyroidism, uremia, and acute intermittent porphyria. Other causes of peripheral neuropathy that may confuse the clinical picture include Guillain-Barré syndrome, amyloidosis, entrapment neuropathies, carcinoid syndrome, paraneoplastic syndromes, and sarcoidosis. Because many of these diseases are treatable, it is imperative that the clinician exclude them before attributing a patient’s symptoms solely to diabetes.

Intercostal neuralgia and musculoskeletal causes of chest wall and subcostal pain may also be confused with diabetic truncal neuropathy. In all these conditions, the patient’s pain may be erroneously attributed to cardiac or upper abdominal disease, thus leading to unnecessary testing and treatment.