Carnett’s Legacy: Raising Legs and Raising Awareness of an Often Misdiagnosed Syndrome

Abstract

Nearly 90 years ago, John Carnett, a Philadelphia surgeon, wrote that chronic right-sided abdominal pain resulting in appendectomy actually originated in the abdominal wall, naming it ‘‘intercostal neuralgia.’’ He detailed the physical findings, including pinch tenderness of a skin/subcutaneous fat fold, cutaneous hyperesthesia at the painful site, and, remarkably, focal tenderness when the abdominal muscles are relaxed and when voluntarily tensed by raising the head or straightened lower extremities off the examination table, now known as a positive Carnett test or Carnett sign [1]. The disorder he described, abdominal wall pain (AWP), has been recognized subsequently to originate anywhere in the abdomen, especially in the lateral border of the rectus abdominis or in a surgical scar, and may occur at multiple sites [2, 3]. A commonly proposed pathophysiology is abdominal cutaneous nerve entrapment (ACNE), chiefly involving the anterior cutaneous branch of a lower thoracic subcostal nerve [4]. The term AWP also sometimes encompasses other nonvisceral disorders, including hernias, thoracic radiculopathy, and myofascial, costal margin, and xiphoid pain [5]. I limit the term AWP to designate what Carnett described, which some authors term ACNE. Experienced physicians accurately predict many cases when a patient, usually a woman, initially says ‘‘I have a constant pain right here,’’ pointing to a spot on her abdomen with one or two fingers. Carnett emphasized the examiner should maintain finger pressure at the tender site when the patient raises the head or legs. For a positive Carnett test, Greenberg and colleagues require increased tenderness with muscle tensing, not just Carnett’s ‘‘almost or quite as much’’ criterion [2]. Their AWP diagnostic criteria are: (1) localized pain or a fixed location of tenderness and (2) superficial tenderness or point tenderness B2.5 cm in diameter or a positive Carnett test. Pain relief after injection of a local anesthetic confirms the diagnosis [2]. I routinely assess tenderness when patients separately elevate their head and legs, as some report increased tenderness by only one of these maneuvers. After reviewing follow-up studies, Greenberg’s group concluded that by adhering to their diagnostic criteria and by following patients over time, visceral causes of pain would seldom be missed [2]. Warning signs are important; for example, 4 (2.9 %) of 137 cases I diagnosed at Kaiser Permanente Southern California were subsequently diagnosed with a visceral source, of whom 3 had unintentional weight loss [3]. Despite the simplicity and accuracy of physical diagnosis, AWP is widely unrecognized: It is suspected by few referring physicians among my patients [3] and in other series [2]. Gastroenterologists and medical residents often overlook the diagnosis [2]; [85 % of surveyed surgeons and residents had not heard of ACNE [6]. Although information on the prevalence and the healthcare costs of AWP and ACNE is limited by underdiagnosis, AWP is commonly diagnosed as a cause of abdominal pain in patients referred to gastroenterologists and to chronic pain clinics [2]. A female predominant syndrome, AWP comprised 7.8 % of symptomatic referrals to me at Kaiser, nearly 50 % the rate of referral for irritable bowel syndrome (IBS) [3]. Patient characteristics included 45.8 % overweight (body mass index [BMI] 25–29.9 kg/ m), 38.1 % obese (BMI[ 30 kg/m) and chronic low back pain, gastroesophageal reflux disease, IBS, and depression, each affecting over 20 % of patients [3]. Dutch & George F. Longstreth gflongstreth@gmail.com