Inferior gluteal pain with sitting, unrelated to ischial bursitis

Abstract

A 64-year-old woman presented to an academic medical centre with postoperative left ischial pain following a left total hip replacement. Her pain was exacerbated by sitting down and with forward flexion of the spine, and the pain radiated from the left ischial tuberosity to the left perineum, groin and medial thigh. An ischial bursa injection was performed, but only resulted in 1 day of excellent pain relief. A diagnosis of inferior cluneal neuralgia was then made. Subsequent inferior cluneal nerve radiofrequency ablation was performed, and provided sustained 50% relief in pain. The patient had a concomitant sensation of ‘ball like’ pressure at her rectum which was determined to be due to levator ani syndrome. She was prescribed pelvic floor physical therapy and botulinum toxin injection, which resulted in further notable improvement of her symptoms.

Background

A common cause of lower buttock pain that is exacerbated by sitting is ischial bursitis. This is a condition amenable to conservative treatments such as physical therapy, use of pressure relieving pillows, home exercise, over the counter anti-inflammatory medications and corticosteroid injection if necessary. However, refractory buttock pain can exist, largely due to concomitant conditions and misdiagnoses. The pathologies underlying buttock pain vary from ischial bursitis to coccydynia, and differentiating between these diagnoses is not always easy. We present a case of buttock pain over the ischium that is not secondary to ischial bursitis.

Case presentation

A 64-year-old woman presented to an academic outpatient physical medicine and rehabilitation clinic with postoperative left buttock pain on 13 August 2020. She had undergone a left total hip replacement on 19 February 2020. Towards the end of March 2020, she began having sharp, 8–9 out of 10, pain that was exacerbated by sitting down and bending over. The pain began in the lower buttock, over the region of the left ischium, and occasionally radiated to left perineum, groin and medial thigh.

Prior to visiting our clinic, the patient’s existing workup included an MRI of the left hip and pelvis which did not offer any pathologic or anatomic reason to explain her pain. Furthermore, she had trialled over the counter non-steroidal anti-inflammatory drugs, tramadol, gabapentin and a corticosteroid dose pack, all with minimal relief. She had also previously been referred to an interventional radiologist who performed a left ischial bursa injection on 8 July 2020. Following the injection, the patient had only 1 day of pain relief before her pain returned to baseline.

On our physical exam evaluation, the patient had tenderness to palpation at left ischial tuberosity, which was exacerbated by passive hip flexion. She had no tenderness to palpation at the bilateral sacroiliac joints or to the piriformis muscles. FADIR test (flexion, adduction and internal rotation) was negative. Sensation to light touch was intact over the left buttock and thigh.

Differential diagnosis

Based on this patient’s history and physical examination, ischial bursitis is a reasonable part of the differential diagnoses and can be confirmed by local injection. However, if corticosteroid injection offers only temporary pain relief, other disorders sharing a similar presentation should be entertained. Local nerve injury¹ or impingement must be considered. Coccydynia is another painful condition that is exacerbated by sitting, however, it is located at the coccyx. Piriformis syndrome or deep gluteal syndrome^{1 2} can be ruled out in this case due to a lack of sciatica, absence of tenderness around the sciatic notch, negative FADIR test and given the more distal nature of this patient’s pain. Pudendal neuralgia is also on the differential, but involves more perineal and pelvic pain than ischial pain.

Treatment

While no optimal treatment algorithm for inferior cluneal neuralgia has ever been proposed largely due to a paucity of clinical evidence, empirical regimen include conservative and surgical approaches.³ In addition to aforementioned conservative treatments, the patient received an ischial bursa injection prior to presentation that provided 1 day of pain relief. This injection confirmed the location of her pain, while suggesting that the aetiology of her pain was unlikely to be bursitis given the short duration of pain relief. Since the patient reported concomitant perineal discomfort, we discussed with her our suspicion for inferior cluneal neuralgia. The patient was amenable to left inferior cluneal nerve (ICN) radiofrequency ablation (RFA), which was performed on 7 October 2020. Considering the proximity of pudendal nerve and one of its branches, the inferior rectal nerve to the perineal branch of the ICN, we ensured our RFA active tip was placed posterolateral to the ischial tuberosity to avoid denervation of these nerves.

Outcome and follow-up

After RFA, the patient reported greater than 50% pain relief, from 8 to 9 out of 10 to 3–4 out of 10 on Numeric Rating Scale, at her 6-month follow-up visit. Based on the evaluations by her physical therapist, her Patient Specific Functional Scale score increased from the initial 1.33 (bending forward 1, sitting 0 and stairs 3) before the RFA to 6 (bending forward 7, sitting 5 and stairs 6) on 19 July 2021. Her remaining discomfort was localised to the rectum. She was subsequently seen by a gastroenterologist who diagnosed her with levator ani syndrome and asked her to initiate pelvic floor physical therapy and exercises. The patient is now undertaking botulinum toxin injection along with the physical therapy for rectal discomfort.

Discussion

This case reinforces the complexity of determining the aetiology of ischial/pelvic pain that is exacerbated by sitting, as it is often the result of multiple aetiologies. While ischial bursitis, with or without proximal hamstring tendinopathy, is a common cause of ischial pain, local nerve injury⁴ with impingement or irritation is another aetiology that must be considered. The ICN arises from the posterior femoral cutaneous nerve (PFCN) of the thigh, travels through the sciatic notch with the sciatic and pudendal nerves, and finally branches off near the gluteal fold to innervate the distal part of the buttock,^{5 6} Dellon reported 17 cases of pain with sitting due to injury of the PFCN. Resection of the inferior cluneal branches and perineal branch resulted in good to excellent outcomes in 76% of carefully selected patients,⁴ which was corroborated by a later study with 52 patients.⁷

In this case, the patient presented with perineal discomfort and a ‘ball-like’ sensation in the rectum, which made the diagnosis of inferior cluneal neuralgia more likely than ischial bursitis. Furthermore, she only had 1 day of pain relief with ischial bursa injection, which again supported a diagnosis of ICN neuralgia. In addition to the pudendal nerve, the PFCN also provides sensory innervation to the perineum via its branches.⁶ The ICN becomes the perineal branch which innervates the lateral perineum, proximal medial thigh, the posterior lateral aspect of the labia majora or scrotum and the clitoris or penis. The ICN communicates with the inferior rectal nerve that arises from the pudendal nerve, which explains the ‘ball-like’ rectal sensation in our patient. The inferior rectal nerve also provides motor innervation to the external anal sphincter and the levator ani,⁶ which explains why our patient got further relief of her symptoms with exercises aimed to strengthen the pelvic floor musculature.

The aetiology of this patient’s ICN neuralgia remains unknown. She underwent a left total hip replacement with anterolateral (Watson-Jones) approach, which suggests that direct injury to the ICN is less likely. The onset of pain, 1 month after procedure, also makes it less likely that her pain was directly related to surgery. However, we cannot rule out postoperative changes to the surrounding anatomy with secondary nerve entrapment, and/or postsurgical inflammatory neuropathy. The concomitant levator ani syndrome in this case is attributed to the ICN’s communication with the inferior rectal nerve, though other aetiologies cannot be ruled out.

The treatment of ICN impingement/neuralgia is mainly conservative, including over the counter pain medicine, prescription neuropathic pain medication, such as gabapentinoids and antidepressants, injections and surgical release for refractory cases.^{4 6} In this case, RFA was effective.

Patient’s perspective.

It is now 17 months from the onset of pain. The chronic pain has influenced the quality of my life and has greatly reduced the ability to participate in previously enjoyed activities. I have been seen by many doctors to diagnosis and treat the pain. While the initial pain has lessened after ablation, the pain from levator ani syndrome has recently increased, for which I am in a course of treatment, including physical therapy, muscle relaxants and botulinum toxin injection.

Learning points.

• Ischial tuberosity pain is not always due to ischial bursitis.

• Inferior cluneal neuralgia may mimic ischial bursitis.

• Perineal pain, including levator ani syndrome, could be one of the presentations of inferior cluneal neuralgia.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s)