The NMJI

Differentiating traumatic neuritis from poliomyelitis
I read with interest the recent article by H. V. Wyatt.1 He has discussed an important issue of traumatic neuritis (TN) due to intramuscular injections and the need to differentiate this entity from cases of poliomyelitis. I would like to make certain observations.

TN following an intramuscular injection in the gluteal region is well known.2 The duration between the administration of injection and onset of paralysis varies from one hour to five days.3 The common peroneal division of the sciatic nerve is more commonly involved as compared to the tibial nerve. Patients usually present with a foot drop due to weakness of the ankle dorsiflexors. Ankle evertors are also weak. The distal groups of muscles are thus predominantly affected. In addition, patients also have sensory impairment in the distribution of the peroneal nerve, namely, the lateral aspect of the leg and foot and the dorsal aspect of the foot.

In contrast, poliomyelitis is a pure motor disorder and sensations are not affected. The pattern of the muscles involved also differs from that of TN. In poliomyelitis, the quadriceps, hip adductors and tibialis anterior are more commonly affected.4 Therefore, the presence of proximal weakness and absence of sensory involvement in a child would favour poliomyelitis as against TN.

The postulated mechanisms of traumatic nerve injury include direct needle trauma, secondary constriction by a scar, ischaemia to the nerve, and direct nerve fibre damage by neurotoxic chemicals in the injected agent.5,6 Introduction of infection or abscess formation due to the use of unsterile injections could be contributory mechanisms.

Intramuscular injection as a risk factor for paralytic poliomyelitis is well known.7,8 This is referred to as provocation paralysis.9 The postulated mechanism is that skeletal muscle injury induces retrograde axonal transport of the poliovirus, thereby facilitating viral invasion of the central nervous system and the progression of spinal cord damage.9 Intramuscular injections also increase the risk of oral polio vaccine-associated paralytic poliomyelitis.10

Unnecessary intramuscular injections should be avoided. Oral drug therapy should be promoted. If an injection is a must, the site should be the lateral aspect of the thigh rather than the gluteal region. A detailed neurological examination is helpful in differentiating TN from poliomyelitis.