Unusual case of lower back pain-piriformis myositis: a case report and literature review

We present a case of a 37-year-old male security officer with fever, severe low back pain radiating to left lower leg and diminished mobility for 1 week. His Lumbar spine X-ray was unremarkable, but his inflammatory markers including CRP, ESR and Neutrophils were high. CT scan with contrast showed rim enhancing fluid collection within the left obturator foramen with inflammatory change in the mesorectal fat. Confirmatory MRI scans depicted inflammatory change in the left piriformis muscle and a localized collection without any abnormality in the spine. Urgent CT guided aspiration was performed and the sample sent for microbiological analysis. Intravenous antibiotics commenced and continued for two weeks with complete resolution.


Introduction
More than half of all the adults experience low back pain (LBP) at some point in their life, being one of the most common cause of scheduled physician visit [1,2]. Pyomyositis of pelvic muscle is a rare cause of LBP with an increased morbidity and disability.
Inflammatory changes in piriformis, more commonly due to fall or infection, can compress sciatic nerve causing sciatica in patients. We present a case with pyomyositis of left piriformis muscle who presented with low back pain and sciatica.

Patient and observation
A 37-year-old male Caucasian security officer presented to our emergency department with severe low back pain for seven days radiating to the left lower limb with an associated single episode of urinary retention and constipation. He also complained of difficulty in walking from a day before. On further inquiry, the patient was generally healthy with no significant medical and surgical history.
On examination, he was febrile 38.5°c, but no chills and rigors.
Straight leg raising test was negative with marked tenderness at the posterior aspect of the left hip joint. Neurological examination revealed mild decrease in muscle power at the left lower limb in L4, L5 and S1 nerve root distribution (Left L4, L5 and S1 power was 4/5). Hematological investigations showed total white blood count (10.7*10^9/l) with 85% neutrophils (9.10*10^9/l) and raised inflammatory markers: erythrocyte sedimentation rate (ESR) (81mm 1 st hour) and C reactive protein (CRP) (528mg/l). His electrolytes and lactate levels were within normal limits. The plain radiograph images of his lumbar spine, pelvic and hip x-rays were

Discussion
Pyomyositis, also known as tropical pyomyositis, is usually prevalent but not limited to Africa and south pacific [3]. Pyomyositis of piriformis is an uncommon variant of muscular pyomyositis. There is no specific age and sex predominance, and the cases are distributed equally. There are reported cases of piriformis myositis in a swimmer, tennis and rugby player, as a probable consequence of a sport induced trauma [4][5][6]. Our patient was a security officer and denied any discernible history of recent trauma prior to the onset of symptoms. Although rare, pyomyositis of piriformis in children can present with characteristic "pinpoint pain" [7]. Compressive symptoms owing to inflammatory swelling can lead to piriformis syndrome and sciatica, a shooting down of pain from sacro-lumbar region towards the buttocks. Our patient presented with a severe low back pain for a week which radiated to left lower limb. The diagnosis of pyomyositis is largely based on strong clinical suspicion.
Proper clinical diagnosis is challenging as the infection is deep, making palpation or even needle aspiration more difficult.
Inflammatory blood markers are helpful but with diagnostic limitations. Very high levels of CRP without definitive clinical findings support non-rheumatic causes like infection or malignancies. Raised inflammatory markers should be investigated aggressively in these patents with different modalities including advanced radiological test to rule out malignancy and potential infections. CRP was raised in our patient but the blood culture was negative.
Ultrasonography can be useful in evaluating suspected abscesses but it may not be able to determine the extent of bony involvement.

Conclusion
Pyomyositis of piriformis should be considered in a patient with low back pain, sciatica and associated inflammatory symptoms.
Although it is a rare infective disease, it attains a complete resolution if treated promptly with intravenous antibiotics. But diagnostic delay can result in deep abscess formation, sepsis and even death. Therefore, it is important for the healthcare workers to have a high diagnostic index for early diagnosis to prevent potential complications and disabling neurovascular compression.

Competing interests
The authors declare no competing interests.

Authors' contributions
Ahmed Elhagar was the attending physician of the present patient.