Baystate Health

Julio A. Martinez-Silvestrini

Through this article, dr. Julio A. Martinez-Silvestrini, medical director at Baystate health, explores the evolving understanding of lateral cutaneous neuropathy (lines) and its role in diagnosing atypical pelvic and trunk pain. He discusses how this often-overlooked entrapment neuropathy presents with sensory disturbances, highlighting the importance of a thorough history, neuromusculoskeletal examination, and diagnostic techniques to differentiate lines from other musculoskeletal or visceral conditions.

Dr. Martinez-Silvestrini also examines key diagnostic criteria, including localized tenderness, altered skin sensation, and the “pinch” test, while emphasizing the role of ultrasound imaging and targeted interventions such as perineural hydro dissection, steroid injections, and cryoablation in both confirming and treating the condition. He concludes by advocating for greater awareness of cutaneous neuropathies as part of the differential diagnosis for patients with persistent, unexplained pain, ensuring more accurate assessments and improved patient outcomes.

The lateral cutaneous nerve entrapment syndrome (LACNES) is an atypical cause of flank, lateral trunk, or superior pelvic pain. As with any other type of entrapment neuropathy, patients may complain of local pain, numbness, tingling, neuropathic pain, or even allodynia in the nerve territory, including the flank and lateral superior abdomen or pelvis.

A good strategy a practitioner can use to figure out the location of the pain is asking the patient to “touch with one finger your most tender area.” In my practice, I’ve noticed that terms like groin, hip and loin tend to overlap, depending on the patient, for which just asking the patient where the pain is may be misleading.

The location of their pain can characterize the origin of pain in most patients complaining of pelvic symptoms. The first step when evaluating patients with pelvic pain is to exclude intrapelvic or intraabdominal pathology and other pain sources like fractures or tumors. Changes in bowel or bladder habits or control, bloating, pain during sexual intercourse, changes in urine or fecal color, weight loss, fever, or chills are common symptoms that will direct the practitioner toward these entities.

Once those other severe conditions have been discarded, we should decide if the patient's symptoms are related to a musculoskeletal injury. Patients with musculoskeletal anterior pelvic pain may have a lower abdominal muscle strain, also known by the non-medical population as a sports hernia. A true abdominal hernia with intraabdominal contents may not present with pain unless the abdominal content is incarcerated or there is an acute abdominal wall defect. Most patients with abdominal hernia will complain of pressure or pinching sensation in the abdominal or inguinal region with an associated soft tissue bulge, usually in the areas around the umbilicus or inguinal ligament where the abdominal wall is thinner. This bulging usually worsens when the patient strains or performs a Valsalva maneuver. Osteitis pubis is another cause of anterior pelvic pain, commonly seen in long-distance runners. Posterior pelvic pain may be referred from the spine, precisely the low lumbar articular facets, known as facet syndrome or lumbar spondylosis. Posterior pelvic pain may also originate from the sacroiliac joint or gluteal musculature. These patients with gluteal or sacroiliac joint pathology usually will also experience radicular symptoms (often described by patients as “sciatica”) in the lower extremities. Lastly, ischial bursitis or proximal hamstring tendinopathy may also be a reason for inferior gluteal or proximal thigh pain.

“Cutaneous Neuropathies Should Also Be Considered In Patients With Symptoms In Areas That Do Not Correlate With Or Involve Commonly Injured Regions, Such As The Spine, Muscles, Ligaments, Tendons, Or Joints”

In patients with predominantly lateral pelvic pain, it may be consistent with lateral thoracic cutaneous branch neuropathy, also known as lateral cutaneous nerve entrapment syndrome or LACNES. The location of pain will not be consistent with the classic clinical presentation of trochanteric bursitis, which involves the lateral hip or cluneal neuropathy, which is usually posterior and superior at the iliac crest border. These lateral thoracic cutaneous nerves arise from the thoracic intercostal nerves between the 7th and the 12th rib, and its branches innervate the lateral skin of the lower thoracic region laterally to the iliac crest. The lateral cutaneous branches of the rami are superficial to the iliac crest and easily accessible for palpation.

The rest of the inferior chest and abdominal innervation include the anterior cutaneous nerves, which usually innervate the anterior part of the trunk. In contrast, the posterior cutaneous nerve innervates the dorsal region. Other commonly discussed iliac or pelvic neuropathies in the medical literature include ilioinguinal nerve injury after iliac crest biopsy or bone graft harvesting, which is beyond the scope of this article.

According to Ishizuka and collaborators, in the American Journal of Medicine in 2021, LACNES is characterized by the following three features: constant area of tenderness located in the flank, covering a fingertip-sized point of maximal pain in the midaxillary line; a larger area of altered skin sensation such as hypoesthesia, hyperesthesia, or altered calm perception covering the pain point, but not necessarily corresponding to a specific complete dermatome; and a positive “pinch” test.

In 2017, Maatman and colleagues described the “pinch” test as pain when “pinching” the skin overlying the painful area using the thumb and index finger. This pain will be worse on the affected side than on the contralateral side.

This type of entrapment neuropathy is not only seen at the iliac crest, but cases involving the lateral trunk at the midaxillary line may also be secondary to LACNES. Lesions to the anterior and posterior cutaneous nerves may also be present, with symptoms in the corresponding dermatomes, anterior abdominal wall/inferior chest or thoracic back, respectively.

An experienced sports medicine or musculoskeletal medicine specialist, such as a physiatrist, can study these nerves under ultrasound imaging. Current advances in this medical imaging modality have made musculoskeletal ultrasound portable and more accessible to clinical practitioners, improving the diagnostic capabilities and ability to provide diagnostic and therapeutic interventions for these patients. A routine abdominal or pelvic sonographic study focuses on intraabdominal and pelvic organs, not superficial or cutaneous structures. Ordering a standard ultrasound will not diagnose this entity but will be helpful in the differential diagnosis. Diagnostic blocks using local anesthetics can be performed to confirm the diagnosis. Other therapeutic procedures, like perineural hydrodissection, perineural steroid injections or nerve cryoablation, can be done under sonographic guidance and provide the patient with relief or curative treatment.

LACNES is an atypical type of neuropathic injury that presents with a predominantly sensory disturbance involving the trunk or superior pelvis, which may be aggravated with certain activities. A detailed history and neuromusculoskeletal examination are vital to rule out other potential entities with similar clinical presentation.

The clinical criteria of this and other trunk cutaneous neuropathies include:

1. A small tender area on the midaxillary line

2. Neuropathic disturbance of the corresponding dermatome and

3. A positive “pinch” test

This diagnosis involving cutaneous nerves should be considered part of the differential diagnosis of pain that appears more discrete and refractory to conventional treatments. Cutaneous neuropathies should also be considered in patients with symptoms in areas that do not correlate with or involve commonly injured regions, such as the spine, muscles, ligaments, tendons, or joints.