Case of The Month

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A 14-months-old, developmentally normal boy presented with complaints of fast breathing and change in voice for 2 days without any upper respiratory symptoms. Vitals at presentation were: RR: 38/min, SpO2: 90% at room air, PR: 140/min, BP: 96/64mmHg, CFT<3s, warm peripheries, and GCS 11/15. Work of breathing was increased with suprasternal and intercostal retractions, and B/L basal crepitations were present. Abdominal examination was normal. The child was mechanically ventilated i/v/o respiratory failure and encephalopathy. CXR showed Right lower lobe bronchopneumonia. PCR of respiratory secretions was positive for Rhinoenterovirus and Staphylococcus, sputum microscopy showed few gram positive bacilli. Baby was diagnosed as Rhinoenteroviral Laryngo-tracheo-bronchitis with secondary pneumonia and managed accordingly. At 48 hours of admission, pneumonia & encephalopathy improved with minimum ventilator settings, normal CXR & blood gas and was extubated. However, baby developed poor respiratory efforts and desaturation, hence was re-intubated. Repeat blood work for sepsis and pneumonia were negative. Neurology consultation was sought for possible neurogenic etiology of extubation failure on day 4 of admission.

On neurological examination, baby was responsive to verbal commands with paucity of spontaneous body movements. Cranial nerve examination: B/L ptosis & horizontal eye movement restriction (vertical eye movements could not be reliably assessed), normal pupillary reactions, VII & hearing regard were normal. Tone was decreased in all 4 limbs, DTRs and superficial reflexes (plantar & abdominal reflex) were not elicit able, power was 2/5 at shoulders and 1/5 at elbow, wrist, hip, knee and ankle; intercostal weakness was present, tongue fasciculations were absent. Baby had withdrawal to painful stimuli. Meningeal signs were absent.

Q: What differential diagnoses would you consider in this child and how will you investigate?

The clinical database for the baby is Rhinoenteroviral Laryngo-tracheo-bronchitis with secondary pneumonia with B/L ptosis and external opthalmoplegia with areflexia, hypotonia and weakness (distal=proximal in LL, distal>proximal in UL). Differentials to be considered are: Miller-Fischer syndrome (MFS) variant of Gullian Barre Syndrome (GBS), critical illness myopathy/myo-neuropathy and brainstem encephalitis.

Table 1: Salient points for the differentials in Index child
DifferentialsPoints ForPoints AgainstPlan
Miller Fischer SyndromeEncephalopathy EOM weakness Ptosis Normal pupils Weakness AreflexiaPresentation in continuation with an infective illnessNerve conduction study CSF Anti-ganglioside antibodies
Critical illness myopathy/neuropathyUL proximal > distal weakness Sensory examination unreliable, doubtful involvementShort duration of ICU stay (<15 days)

No steroids

Nerve conduction study
Enteroviral BS encephalitisPtosis + EOM restriction WeaknessNormal pupils with expected BS involvement unlikely, pupillary dilation with poor response more likely) Areflexia (Hyper-reflexia expected) Improving encephalopathyMRI brain with contrast

NCS:

  • MFS/GBS -acute demyelinating or axonal motor or sensorimotor polyneuropathy
  • Critical illness myopathy- Axonal motor polyneuropathy
  • Critical illness neuropathy: Axonal sensorimotor polyneuropathy

CSF: Albumino-cytological dissociation in MFS/GBS

Table 2A: Motor Nerve conduction studies

Stimulation DistalProximalFall Interpretation Impression
Right Tibial
Amplitude (mV)3.71.365%Temporal dispersionDemyelination
Area10.76.935.5%
Duration (ms)6.712.485%
NCV (m/s)25Decreased
DL(ms)3.2sNormal
Left Tibial
Amplitude (mV)5.73.047%Temporal dispersionDemyelination
Area25.613.348%
Duration (ms)10.49.211.5%
NCV (m/s)32Decreased
DL(ms)2.5Normal
Right Peroneal
Amplitude (mV)1.80.572%LowDemyelination
Area6.12.362%Conduction  block
Duration (ms)2.67.1173%
NCV (m/s)27m/sDeceased
DL(ms)2.6
Left Peroneal
Amplitude (mV)2.21.341%Temporal dispersionDemyelination
Area9.76.137%
Duration (ms)7.69.018%
NCV (m/s)24Decreased
DL(ms)2.7Normal
Left Median
Amplitude (mV)5.12.649%Conduction  blockDemyelination
Area2311.550%
Duration (ms)9.89.305%
NCV (m/s)34Deceased
DL(ms)1.9Normal
Left Ulnar
Amplitude (mV)4.03.122.5%NormalNormal study
Area16.114.97.5%
Duration (ms)10.511.04.7%
NCV (m/s)48Normal
DL(ms)1.2Normal


F-wave study

F-waves: Not recordable in left ulnar nerves and bilateral peroneal nerves ; Normal in bilateral tibial nerves; Inconsistent (Present in <50% stimulations) in left median nerve

Table 2B: Sensory nerve conduction studies

Stimulation Interpretation Impression
Left Median Sensory
Amplitude (µV)21Normal (24 + 7.3)Normal study
NCV(m/s)57Normal
DL(ms)1.2Normal
Left Ulnar sensory
Amplitude (µV)16NormalNormal study
NCV(m/s)57Normal
DL(ms)1.1Normal
Right SuralNot recordable
Left Sural Not recordable

Q: How do you interpret the NCS study values?
We interpret the NCS criteria according to the following principles:

Table 3: Interpretation of nerve conduction studies

Distal vs proximal stimulation
Demyelination
Amplitude loss*>20%
Area loss*>50%Conduction block
Area loss *>20%, <50%Temporal dispersion
Increase in CMAP duration*>15%Temporal dispersion
(* % changes of values b/w distal & proximal site stimulations)
Distal latency>130% of upper limit of normalDemyelination
Nerve conduction velocity (NCV)<75% of lower limit of normal or

<35m/s in upper limbs/ <30m/s in lower limbs

Demyelination
Axonal pattern
CMAP amplitudeLow
Distal latency<130% of upper limit of normal
Nerve conduction velocity (NCV)>75% of lower limit of normal or

Criteria for acute inflammatory demyelinating polyneuropathy (AIDP):

Atleast 2 of the following in 1 nerve incase all other nerves are in-excitable and the distal CMAP (dCMAP) is >10% of lower limit of normal (LLN)

  1. Motor NCV <90% LL (85% if dCMAP in <50% of LL)
  2. Distal motor latency >110% of upper limit of normal (ULN)
  3. pCMAP/dCMAP ratio <0.5 and dCMAP >20% LLN
  4. F- response latency >120%ULN

Our case had NCS consistent with demyelination in 5 nerves. Lower limb sensory nerves were not elicit able. Hence, NCS was s/o Motor Sensory demyelinating polyneuropathy.

Q: So how does it relate with the clinical differential diagnoses considered?

The NCS pattern is consistent with AIDP or GBS. MFS usually does not have significant limb weakness. This was present in our case in addition to MFS features, hence, diagnosed as MFS-GBS syndrome. Presence of a demyelinating polyneuropathy is against the diagnosis of critical illness myopathy/myoneuropathy. As NCS was definitive, MRI brain was not done. Serum antiganglioside antibodies were negative.

 

Q: How do you manage further?

Child was given IvIg 2g/kg infusion. Weakness gradually improved. By day 10 of admission, baby was tracheostomised, and weaned to room air, proximal upper & lower limb power improved to 3/5 with partial improvement of ptosis. Treatment, outcomes and prognosis is probably similar to GBS.