Diabetic Truncal Neuropathy—Clinical and Radiological Image

• Max Ellenberg coined the phrase diabetic truncal mononeuropathy in 1978 in the inaugural issue of Diabetes Care referring to a diabetic neuropathy affecting nerves of the trunk.

• In a series of 40 cases, the syndrome, characterized by the abrupt onset of severe unilateral pain, raises clinical concern for intrathoracic or intra-abdominal pathology.

• Ellenberg emphasized that diabetic truncal mononeuropathy typically occurs in the setting of long-standing diabetes and had a good prognosis with the pain abating within a few months.

• Ellenberg also emphasized, “There was virtually no motor involvement.”

• This latter assertion has evoked case reports illustrating examples of abdominal protrusions due to abdominal wall muscle weakness associated with diabetic truncal neuropathy.

• Ellenberg, however, did not use electromyography to look for evidence of non–clinically obvious motor involvement in his cases.

• An example of diabetic truncal neuropathy with abrupt onset of excruciating unilateral abdominal pain, unilateral abdominal protrusion, and good prognosis is provided.

• Far from rare, motor involvement in diabetic truncal neuropathy is likely frequent.

A 59-year-old man with a 13-year history of diabetes treated with metformin developed the sudden onset of excruciating and unrelenting right abdominal pain. Initially, he had hypersensitivity to light touch over both sides of the abdomen. An extensive workup revealed no identifiable intra-abdominal pathology. The pain was initially treated with opioids, gabapentin, and pregabalin. After a clinical diagnosis of acute right diabetic truncal neuropathy, treatment for neuralgic pain with carbamazepine and duloxetine was instituted. Four weeks following the onset of pain, a large protuberance of the right anterolateral abdomen developed (Fig. 1A). Abdominal computed tomography demonstrated thinning of multiple right abdominal oblique (external, internal, and transverse abdominis) muscles (Fig. 1B). Electromyography and nerve conduction studies demonstrated a moderately severe generalized sensory axonal and demyelinating peripheral neuropathy. Thoracic and lumbar paraspinal muscles did not demonstrate fibrillations on either side. However, thoracic spine MRI did demonstrate T2 hyperintensity in the most lateral right T12–L1 paraspinal muscles consistent with denervation. Electromyography of abdominal wall muscles was not performed. The presence or absence of abdominal reflexes was not recorded. Cerebrospinal fluid protein was elevated at 102 mg/dL (normal range 15–45). The severe neuralgic pain gradually resolved over 3 months and the abdominal protuberance over 6 months.

Max Ellenberg coined the label diabetic truncal mononeuropathy (1). While Ellenberg did not expressly state his reason for using “mononeuropathy,” an explanation would be to distinguish this entity from the “polyneuropathy” (distal symmetrical generalized peripheral neuropathy) commonly associated with diabetes. Ellenberg described 40 cases occurring in patients with long-standing diabetes and presenting with severe unilateral thoracic or abdominal pain (1). Extensive evaluation for intrathoracic or intraabdominal pathology is unrevealing in this disorder (1). Moreover, the transient nature and good prognosis of the severe pain are characteristic (1). Ellenberg specifically highlighted the absence of motor involvement in diabetic truncal mononeuropathy (1). However, exceptions to that assertion have been reported (2–8). Muscle weakness in diabetic truncal neuropathy has been described as abdominal swelling, hernia, pseudohernia, and abdominal “mass” (2–8). These reports also included evidence of active muscle denervation by electromyopathy (2–8). One year before Ellenberg’s large series, Longstreth and Newcomer reported a small series of four patients with abdominal pain caused by “diabetic radiculopathy” (9). Although lacking clinical evidence of motor involvement, all four patients had active denervation in paraspinal muscles by electromyography (9). Consequently, motor involvement in diabetic truncal neuropathy is likely frequent.

Duality of Interest. No potential conflicts of interest relevant to this article were reported.

Author Contributions. S.E.F. and J.E.R. participated in the conception, research, drafting, revision, and approval of this manuscript. J.E.R. is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.