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Sixty-two-year-old male, no comorbidities, had a new onset seizure, uh, which was a GTCS witnessed and post-ictal confusion, came to the hospital, started him on levetiracetam, uh, and, uh, further investigation, MRI brain and EEG was done. MR... All the elec- basic, uh, investigations, RFT, LFT, electrolytes, everything was normal, within normal limits. And MRI showed bi- caudal hyperintensities, caudate hyperintensities, with little hyperintensities in the insular le- left insular region. EEG showed, uh, Teej showed left temporal slowing, uh, intermittent with, uh, fe- intracranial discharges with phase reversal at, uh, T5. And, uh, basic and all blood basic investigations were normal. And, uh, otherwise patient also-- but one episode of patient became aggressive. So, one, one, uh, Serenase was given. And then next day morning he was okay. As he had one episode of Serenase, uh, and, uh, o-one week of low mood, lumbar puncture was done. CSF glucose normal, cells 2 WBC, lymphocytes, expert MT B negative. Uh, the HSV PCR sent, report awaited. Uh, but protein was elevated, 131. Uh, so CSF autoimmune encephalitis panel was also sent. Uh, so he was started on a, uh, next day morning, after third day, he had one more episode of seizure, query, because we don't know, we have not witnessed, but patient became very drowsy. EEG showed, uh, frequent intracranial discharges. So, he was, uh, loaded with another, uh, uh, anti-epileptic, lacosamide, uh, af - after lacosamide, patient was, uh, still drowsy, was shifted to ICU. In the ICU, patient had one more episode of seizure. So, total three episodes probably. This was witnessed, the third episode, and, uh, valproate was given. Uh, now patient is intubated because of low GCS.

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What's your differential diagnosis at this point?

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Whats differential Ntoday ammonia 161

This is a rich clinical picture. Here's my structured differential with the new ammonia of 161 µmol/L factored in:

Clinical Summary (Key Features)

  • 62M, no comorbidities
  • New-onset GTCS x3, refractory, now intubated
  • MRI: bilateral caudate hyperintensities + left insular T2/FLAIR signal
  • EEG: left temporal slowing, epileptiform discharges phase-reversing at T5
  • CSF: protein 131, cells 2 (lymphocytes), glucose normal, MTB negative, HSV PCR pending
  • Behavioral change (aggression, low mood ~1 week)
  • Ammonia 161 µmol/L (elevated)
  • LFT normal (as stated)

Differential Diagnosis

1. Autoimmune Encephalitis (Top differential)

  • Best explains: subacute behavioral change, refractory seizures, caudate + insular MRI signal, CSF lymphocytic pleocytosis with elevated protein, no infection markers
  • Caudate involvement is characteristic of anti-NMDAR or anti-CASPR2 encephalitis
  • Insular involvement also seen in LGI1 encephalitis (which also causes faciobrachial dystonic seizures and hyponatremia - though Na was normal here)
  • Panel sent - await results
  • Age 62M: also consider paraneoplastic encephalitis (anti-Hu, anti-Ma2) - needs tumor workup (CT chest/abdomen/pelvis, PET if needed)

2. HSV Encephalitis (Must not miss)

  • HSV PCR pending - critical result
  • Classically involves temporal lobes; left temporal EEG changes fit
  • However, caudate involvement is less typical for HSV
  • Insular involvement can occur
  • Empirical acyclovir should already be running - if not, start immediately

3. Hyperammonemic Encephalopathy

  • Ammonia 161 is significantly elevated (normal <50 µmol/L)
  • LFT reportedly normal - raises question of:
    • Valproate-induced hyperammonemia (he was given valproate! - this is a well-known cause of elevated ammonia without LFT abnormality)
    • Occult liver disease not reflected yet in LFT
    • Urea cycle disorder (rare in adults, but late-onset can occur)
    • Urease-producing UTI (less likely without pyuria)
  • Valproate-induced hyperammonemic encephalopathy (VHE) can worsen seizure control paradoxically and cause encephalopathy - this is clinically very relevant here

4. Prion Disease (CJD)

  • Bilateral caudate hyperintensities on DWI/FLAIR is a classic CJD pattern (pulvinar sign, caudate/putamen involvement)
  • Rapidly progressive dementia + psychiatric features + seizures + EEG changes fit
  • CSF 14-3-3 protein, RT-QuIC should be sent if not done
  • Rapidly progressive course supports this

5. Viral Encephalitis (non-HSV)

  • EBV, CMV, HHV-6, enterovirus, arboviral (JE in appropriate epidemiological context)
  • CSF lymphocytosis with elevated protein fits
  • Less characteristic MRI pattern

6. Metabolic/Toxic Encephalopathy

  • The elevated ammonia now makes this a standalone consideration
  • However, the focal MRI changes and epileptiform discharges make a purely metabolic cause insufficient to explain the whole picture

Immediate Action Points

PriorityAction
🔴 UrgentCheck if acyclovir is running - if not, start 10 mg/kg IV q8h empirically
🔴 UrgentConsider stopping valproate - may be contributing to ammonia rise (switch seizure coverage to lacosamide/levetiracetam/clobazam)
🔴 UrgentRepeat ammonia after stopping valproate
🟡 HighSend CSF 14-3-3 and RT-QuIC (for prion)
🟡 HighMRI DWI sequences review - caudate DWI restriction = CJD signal
🟡 HighTumor workup (CT CAP or PET) for paraneoplastic
🟡 HighSend blood autoimmune panel (NMDAR, LGI1, CASPR2, AMPAR, GABABR) in parallel with CSF panel
🟢 PendingAwait HSV PCR, CSF autoimmune panel

Most Likely Diagnosis

Given the full picture: Autoimmune encephalitis (most unifying) with valproate-induced hyperammonemia as a complication. CJD must be actively excluded given caudate signal. HSV must be covered empirically until PCR returns negative.
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