This is a short brief report about 2 patients that didn’t present nodules and low back pain -as many patients do- but other masquerading symptoms such as hip or abdominal pain. The final outcome suggested that back mice primarily caused the pain syndromes.
Curtis et al. present 2 case reports of 2 patients that presented UNUSUAL SYMPTOMS and signs related to one of the STILL OVERLOOKED entities, the back mice. They presented these cases that seem to be related to referred pain, not just to low back pain but also to abdominal or trochanteric pain and tenderness.
Personal notes: The authors do not mention that some of this referred pain can be due to irritation of cutaneous nerves in the low back, such as the lateral branches of the costal XII nerve, iliohypogastric or ilioinguinal nerve that could explain the referred clinic.
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The authors conclude that despite further studies are necessary, many clinicians should consider the ability of back mice to present masquerading other conditions, not just back pain. Especially when it presents as atypical obscure pain.
Fibro-fatty nodules and low back pain
The back mouse masquerade
Peter Curtis et al.
Chapel Hill, North Carolina
The Journal of Family Practice
April 2000 Vol 49, No 4, Page 345
Curtis et al. knowing about any possible cause of low back pain is helpful
They start this article mentioning that the SCIENTIFIC evidence for the specific causation and treatment of low back pain is relatively WEAK (except from the vertebral disk injury).
There are limited evidenced-based interventions, mainly short-term therapy with muscle relaxants and analgesics, and the encouragement to return to daily routines as quickly as possible.
Curtis et al. state that there may be subtypes or syndromes of low back pain, and their experience suggests that one of these causes could be the a FIBRO-FATTY NODULE (back mouse).
Taking the suffering and the cost related to the low back pain into consideration, knowing an identifiable and remediable cause, “the fibro-fatty” nodules and low back pain would always be helpful.
They describe 2 patients that are examples that back mice are a cause of low back pain but that they can be MASQUERADING other clinical problems.
Back mouse masquerading other pains, not just low back pain (they present 2 case reports):
Case 1. BACK MICE presenting as BILATERAL TROCHANTERIC BURSITIS
A 53-year-old nursing aide developed symptoms of trochanteric bursitis following a vaginal hysterectomy in 1985. She suffered from mild hypertension and chronic depression. The HIP PAIN was bilateral and intermittent. It would affect one side and then the other. It was radiating down the legs and limiting her.
Examination reveals marked tenderness to palpation over the great trochanter in either area.
There were no clear precipitating factors.
It was first treated with a variety of nonsteriodeal anti-inflammatory agents, with little effect. Also other therapies such as ultrasound, exercise, cushioned shoes with temporary effect.
Antidepressants improved her depression but not the hip problem.
In 1991 an orthopedic evaluation confirmed the diagnose of BILATERAL TROCHANTERIC BURSITIS. Radiographs showed only mild degeneration of the L4/L5 vertebral disc.
The patient GOT RELIEF for some weeks with direct injection of the bursa with lidocaine and corticoid. They had to be repeated on a regular basis. She also took acetaminophen and oxycodone to help control the pain.
In 1995 she applied for disability.
In 1998 detailed examination of the back revealed 2 long rubbery and tender fibro-fatty nodules, one lying on each iliac crest (3×1 and 6×1 cm).
A REPEATED TESTING ON FIRM PALPATION OF THESE NODULES reproduced the pain over each trochanteric area, where the patient had experienced the pain in the past.
EACH NODULE was treated with multiple puncture of the capsule (6-8 punctures) and injected with 3 cc lidocaine and 40 mg prednisone. THERE WAS IMMEDIATE and complete relief.
After 5 months there were NO SIGNS of clinical trochanteric bursitis, but there were other symptoms.
Case 2. Back mice presenting as abdominal emergency
A 25-year-old woman suffering from diabetes 2 controlled by diet and exercise. Past history of hystererectomy and appendectomy and poliycystic ovaries. She worked as a nurse on the pediatric ward.
In 1997, she was visited for presenting mild low back pain and right-sided lower abdominal pain, which were associated with dysuria and frequency of urination during the previous 2 months.
She had past history of low back pain 2 years earlier.
Her urine test showed mildly positive leukocyte and trace of protein. She took trimethoprim.
Ten days later, she returned reporting much worse abdominal pain, particularly when sitting and lying down. It kept her awake at night. She complained of feeling of fullness in the right lower abdominal quadrant. There were NO changes in bowel habit, no fever, nausea or anorexia.
She was taking NAIDS. A repeated urinalysis was normal. A pelvic examination was normal.
Two days later, the abdominal pain got much severe. It was sharp, intermittent, not colicky and traveled down into the groin and right anterior thigh. Less pain while standing.
Lumbar X-ray showed mild degeneration of the hip joints and some spurring of the inferior aspect of both sacroiliac joints.
Blood test was normal except for a white blood count of 11,200.
Then they suspected of a LOWER ABDOMINAL abscess. The tomography scan was normal except for a left ovarian cyst.
A repeated blood test several hours later showed 13,100 WBC. But the surgeon gave the opinion that it was a musculoskeletal problem.
Then a family medicine resident found a SIGNIFICANT point of tenderness over the right sacroiliac joint. DEEP PALPATION of this area PRODUCED pain radiating to the right inguinal region.
The patient received an injection over the sacroiliac joint of 60 mg ketorolac tromethamine (NSAID), which produced relief and the patient was sent home (there was no clear explanation of the WBC elevation).
Ten days later, the patient was visited again with low back symptoms that were worse when standing. Careful examination revealed an extremely TENDER 3 cm long, partly mobile, fibro-fatty nodule along the mid region of the right iliac crest, 4 inches lateral to the spinous process.
Pressing the nodule firmly made the patient CRY and REPRODUCED the right lower abdominal symptoms.
FOLLOWING MULTIPLY PUNCTURE TECHNIQUE with lidocaine and corticoid (3 cc lidocaine and methyprednisolone acetate 40 mg) the patient experienced IMMEDIATE pain relief with NO MORE abdominal pain, no difficulty to sit or lying down since that time. At least for 2 years there was no recurrence.
The intriguing questions from Peter Curtis
Peter Curtis wonders: Do back mice really exist?
The author insists that there are several publications that demonstrate that the nodules existed in a prevalence maybe around 15% in general population (despite many clinicians do not know about them).
Peter Curtis wonders: Why would back mice masquerade as other conditions?
They related to referred pain. (Personal notes: But Curtis does not seem to relate clearly to the affection of the specific cutaneous nerves such as iliohypogastric, ilioinguinal, or cluneal that have certain known distributions. He does not mention that the clinic of trochanteric pain could be by a phenomenon of referred tenderness neither).
Peter Curtis wonders: Where do back mice come from?
He mentions previous study. Back mice are fat confined in a fibrous capsule, divided by fibrous septa, with some blood vessels and nerve fibers. They usually have a STALK that connects them to the tissues below the deep fascial layers. They can extrude through the deep fascia through the neurovascular foramina in the deep fascia.
Peter Curtis wonders: Why would back mice cause pain?
In his opinion, the good results of MULTIPLE PUNCTURE of the nodules compared to SINGLE PRESSURE technique SUGGEST that the pain could be related to RAISED INTRANODULAR PRESSURE.
Peter Curtis wonders: Why would injections relieve pain caused by back mice?
The fact that in certain studies there is no difference between the lidocaine and saline injection, suggests that the real effect of the injection is the rupture of the capsule that lessens the tension of the innervated fibrous capsule. It could also be because it washes out irritating substances such as substance P or by an interruption of the neural feedback mechanism.
Peter Curtis wonders: Does injection treatment of the back mouse really work?
Curtis admits that there haven’t been randomized controlled trials or long-term follow-up studies.
Published in September 2018 By Marta Cañis Parera
- Curtis P, Gibbons G, Price J. Fibro-fatty nodules and low back pain. The back mouse masquerade. J Fam Pract. 2000 Apr;49(4):345-8. PubMed PMID: 10778841.
- Curtis 1993
- Ries 1937
- Motyka 200
- Swezey 1991
- Copeman 1947
- Collee 1991