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Prolapsed intervertebral disc (PIVD) commonly presents as lower back ache associated with features of radiculopathy. We present an unusual case of a patient presenting with foot drop and our diagnostic and therapeutic protocol for the same. Our patient was a 40-year-old female who was diagnosed as a case of PIVD L4-L5 and was advised for non-operative treatment. During her treatment, the patient received intramuscular analgesic therapy immediately following which the patient reported a foot drop in the left lower limb. While the patient was initially thought to present with an acute neurological worsening of the affected disk requiring urgent decompression. However, post injection nerve palsy was kept as one of the differentials. The diagnosis of post injection palsy was confirmed by obtaining an NCV study and MRI neurography. She was subsequently managed conservatively via a foot drop splint, oral analgesic therapy and neurotropic agents. On follow up at 6 months she had complete neurological recovery. Post injection palsy can mimic as further prolapse of disc in a case of PIVD. It is imperative to differentiate these two as the management follows different course, the differentiation can be done using MR neurography.
Keywords: MR Neurography; Foot drop; PIVD; Post injection palsy
Prolapsed intervertebral disc is one of the common health problems leading to work disability . Many cases of prolapsed intervertebral disc present with back pain and radiculopathy. In patients with prolapsed intervertebral disc at the L4- L5 level, the positive predictive value of sensory deficit is 50%, while motor deficit is present in 54% of the cases . We present a rare case of prolapsed intervertebral disease where the patient presented with foot drop following an intra-muscular injection and the uncommon diagnostic modalities which we used to establish the cause of foot drop.
A 40-year-old female had low back ache for last 3 months. The pain was sharp in character, which increased on standing and movement and decreased on rest. The pain was radiating to right lower limb. She also complained of numbness in right L5 dermatome region. The pain gradually progressed to an intensity of 7/10 and interfered with activity of her daily living. She initially presented to a private practitioner who sought baseline investigations including MRI (Figure 1) and the diagnosis of prolapsed intervertebral disc (L4-L5) was established. Patient was advised for elective discectomy. Initial treatment in the form of oral and intramuscular analgesics was prescribed.
Although the patient had immediate relief from the back ache following intramuscular injection of analgesic, she reported foot drop in left lower limb within minutes of the injection. The treating surgeon at this time suspected rapid progression of neurological deficit secondary to disc prolapse and the patient was suggested to undergo emergent disc removal. It was at this
stage that she presented to our institute, for a second opinion. The
patient was able to walk for long distance without appearance
of pain. On examination, there was no para spinal spasm or list.
The straight leg raising test was asymptomatic bilaterally. The
motor power of left tibialis anterior, peroneus longus, peroneus
brevis, extensor hallucis longus and extensor digitorum longus
were 0/5 as per MRC grading. The motor power in other group
of muscles of left lower limb was normal (5/5). There was no
sensory deficit in the left lower limb.
Although rapid worsening of neurology in the patient
could suggest further prolapse of the involved disc, it was the
sudden relief in pain which provoked us to seek answers beyond
prolapsed disc. Another possibility which could explain the
symptoms was post injection nerve injury. The management
of neurological worsening due to further prolapse of disc is
emergent decompression while post injection palsy can be
managed over conservative lines. In view of these two radically
different treatment methodologies for each of the individual
diagnoses, we obtained nerve conduction velocity studies with
the aim to establish a diagnosis. The NCV revealed motor axonal
involvement of left common peroneal nerve.
The MR neurography of hip joint revealed soft tissue around
sciatic nerve (due to fibrosis) (Figure 2). The diagnosis of post
injection palsy of peroneal component of sciatic nerve was thus
Patient was further managed conservatively on foot
drop splint, oral analgesics and neurotrophic agents. Clinical
examination one month later revealed improved power at tibialis
anterior, EHL and EDL. However, motor power in peroneus
longus and peroneus brevis was still 0/5. Patient was kept
under regular follow up for appreciation of further neurological
recovery. At 6 months of follow up, clinical examination revealed
complete neurological recovery with power of 5/5 in all muscles
of the anterior and lateral compartment. Informed consent was
taken from the patient for publishing this case.
Radiculopathy from lumbar disc herniation can be a result
of mechanical compression, ischemia or inflammatory irritation
of the nerve root. Oral and intramuscular analgesics are widely
used for initial management of slipped disc. However it was
indeed unfortunate that management of one pathology led to the
development of another pathology.
The World Health Organization reported that around 12
billion injections are administered every year and 50% of them
are unsafely administered . Sciatic nerve is the most common
nerve to be affected following intramuscular injection [4,5].
Around 90% of patients with sciatic nerve injury have immediate
onset of symptoms [6,7]. Motor function is more severely affected
compared from sensory component . Peroneal division is more
frequently involved, and foot drop is most common presentation
due to weakness in dorsiflexion and eversion [4,9-10].
Although there is a huge burden of post injection palsy,
the condition is frequently underdiagnosed due lack of clinical
suspicion. Clinical examination supplemented with nerve
conduction velocity study is useful in diagnosis of sciatic
nerve injection injury ; however, they cannot define the
precise location of the site of nerve lesion. Magnetic resonance
neurography (MRN) is a new technique which allows detection
of peripheral nerve injury and can reveal neural injury even on
fascicular micro-structural level . Kline et al.  reported
spontaneous recovery in 68 % patients who had common
peroneal division injury following post injection sciatic nerve
injury . Kakati et al.  also reported favorable outcome in
patients with post injection palsy with partial deficits, however
external and internal neurolysis may be needed if spontaneous
recovery is not observed with non-operative management.
The article also reinforces the art and importance of history
taking and the importance of building differentials before
initiation of treatment. It was only after careful history taking
we could suspect the cause of foot drop in a patient of prolapsed
intervertebral disc to be post injection sciatic nerve involvement.
Prolapsed disc is treated by discectomy and decompression while
post injection palsy is best managed by non-surgical modalities.
If post injection palsy was not suspected, the patient would have
been at the receiving end of surgical intervention which was not
needed for her.
The article also reinforces the importance of knowing safe
corridors for gluteal injection. Understanding of the anatomic
course of sciatic nerve and proper training is a must to avoid
such instances in future. In gluteal region, the ventrogluteal area
(gluteal triangle as depicted in Figure 3) is safer with only one
reported complication . The subcutaneous fat is less at this
site, with high bulk of gluteus muscle. Even after extensive search in the literature, we could not find
similar report of post injection palsy in a patient of prolapsed
intervertebral disc leading to neural deficits. Also, there is no
literature emphasizing importance of MR neurography in such