MRI in a case of adult-onset citrullinemia

Advances in urea cycle neuroimaging: Proceedings from the 4th International Symposium on urea cycle disorders, Barcelona, Spain, September 2013

Our previous imaging research performed as part of a Urea Cycle Rare Disorders Consortium (UCRDC) grant, has identified specific biomarkers of neurologic injury in ornithine transcarbamylase deficiency, OTCD. While characterization of mutations can be achieved in most cases, this information does not necessarily predict the severity of the underlying neurological syndrome. The biochemical consequences of any mutation may be modified additionally by a large number of factors, including contributions of other enzymes and transport systems that mediate flux through the urea cycle, diet and other environmental factors. These factors likely vary from one patient to another, and they give rise to heterogeneity of clinical severity. Affected cognitive domains include non-verbal learning, fine motor processing, reaction time, visual memory, attention, and executive function. Deficits in these capacities may be seen in symptomatic patients, as well as asymptomatic carriers with normal IQ and correlate with variances in brain structure and function in these patients. Using neuroimaging we can identify biomarkers that reflect the downstream impact of UCDs on cognition. This manuscript is a summary of the presentation from the 4th International Consortium on urea cycle disorders held in, Barcelona, Spain, September 2, 2014.

Hyperammonemic coma in a post-partum patient with undiagnosed urea cycle defect

Urea cycle disorders (UCD) are common during neonatal period, and it is rarely reported in adults. We are reporting a patient presenting with post-partum neuropsychiatric symptoms rapidly progressing to coma. Markedly raised serum ammonia level on presentation with an initial normal magnetic resonance imaging (MRI) of brain and normal liver function tests led to the suspicion of UCD, which was confirmed on the basis of urine orotic acid and elevated serum amino acid levels. We had to resort to hemodialysis to correct the hyperammonemic coma, which was unresponsive to conventional anti-ammonia measures. She exhibited remarkable improvement with a progressive decline in serum ammonia with repeated hemodialysis and made a full recovery. Timely diagnosis and early institution of hemodialysis in the setting of a poor neurological status maybe considered a suitable treatment option.

Urea cycle disorders: brain MRI and neurological outcome

BACKGROUND

Urea cycle disorders encompass several enzyme deficiencies that can result in cerebral damage, with a wide clinical spectrum from asymptomatic to severe.

OBJECTIVE

The goal of this study was to correlate brain MRI abnormalities in urea cycle disorders with clinical neurological sequelae to evaluate whether MRI abnormalities can assist in guiding difficult treatment decisions.

MATERIALS AND METHODS

We performed a retrospective chart review of patients with urea cycle disorders and symptomatic hyperammonemia. Brain MRI images were reviewed for abnormalities that correlated with severity of clinical neurological sequelae.

RESULTS

Our case series comprises six urea cycle disorder patients, five with ornithine transcarbamylase deficiency and one with citrullinemia type 1. The observed trend in distribution of brain MRI abnormalities as the severity of neurological sequelae increased was the peri-insular region first, extending into the frontal, parietal, temporal and, finally, the occipital lobes. There was thalamic restricted diffusion in three children with prolonged hyperammonemia. Prior to death, this site is typically reported to be spared in urea cycle disorders.

CONCLUSION

The pattern and extent of brain MRI abnormalities correlate with clinical neurological outcome in our case series. This suggests that brain MRI abnormalities may assist in determining prognosis and helping clinicians with subsequent treatment decisions.

Acute hyperammonemic encephalopathy in adults: imaging findings

BACKGROUND AND PURPOSE

Acute hyperammonemic encephalopathy has significant morbidity and mortality unless promptly treated. We describe the MR imaging findings of acute hyperammonemic encephalopathy, which are not well-recognized in adult patients.

MATERIALS AND METHODS

We retrospectively reviewed the clinical and imaging data and outcome of consecutive patients with documented hyperammonemic encephalopathy seen at our institution. All patients underwent cranial MR imaging at 1.5T.

RESULTS

Four patients (2 women; mean age, 42 ± 13 years; range, 24-55 years) were included. Causes included acute fulminant hepatic failure, and sepsis with a background of chronic hepatic failure and post-heart-lung transplantation with various systemic complications. Plasma ammonia levels ranged from 55 to 168 μmol/L. Bilateral symmetric signal-intensity abnormalities, often with associated restricted diffusion involving the insular cortex and cingulate gyrus, were seen in all cases, with additional cortical involvement commonly seen elsewhere but much more variable and asymmetric. Involvement of the subcortical white matter was seen in 1 patient only. Another patient showed involvement of the basal ganglia, thalami, and midbrain. Two patients died (1 with fulminant cerebral edema), and 2 patients survived (1 neurologically intact and the other with significant intellectual impairment).

CONCLUSIONS

The striking common imaging finding was symmetric involvement of the cingulate gyrus and insular cortex in all patients, with more variable and asymmetric additional cortical involvement. These specific imaging features should alert the radiologist to the possibility of acute hyperammonemic encephalopathy.

Adult nonhepatic hyperammonemia: a case report and differential diagnosis

This article presents a case report of nonhepatic hyperammonemia, i.e., elevated serum ammonia secondary to a nonhepatic etiology. It then discusses the importance of broadening one's differential diagnosis to include such nonhepatic causes of elevated ammonia levels, and provides a short review of rarer causes of hyperammonemia in the adult population. Treating the underlying condition is the best way to prevent recurrence of hyperammonemia. However, symptomatic treatment should not be delayed while investigating the underlying source.

Magnetic Resonance Imaging Findings in Bilateral Basal Ganglia Lesions

Introduction: Radiologists may encounter bilaterally symmetrical abnormalities of the basal ganglia on magnetic resonance imaging (MRI), typically in the context of diffuse systemic, toxic or metabolic diseases. A systematic approach and broad knowledge of pathology causing this uncommon group of conditions would be useful. Materials and Methods: This review uses illustrative images to highlight metabolic conditions, such as Leigh’s syndrome, citrullinaemia, hypoglycaemia or carbon monoxide poisoning, as well as other causes of bilateral basal ganglia lesions such as osmotic myelinolysis, deep cerebral venous thrombosis and Creutzfeldt-Jakob disease. Results: Careful assessment of radiological findings outside the basal ganglia, such as involvement of the cortex, white matter, thalamus and pons, together with clinical correlation, may be helpful in narrowing the differential diagnosis, and directing further radiological, biochemical or genetic investigations. Recent advances in MR technology have resulted in newer techniques including diffusion-weighted (DW) MR imaging and MR spectroscopy (MRS); these may be helpful if appropriately used. Conclusions: Abnormal MRI findings in the basal ganglia should not be interpreted in isolation. A systematic approach including DW MR imaging, MRS, and a broad knowledge of diffuse systemic, toxic or metabolic diseases is helpful. Key Words: Basal ganglia, Metabolic disorders

Cranial MRI in acute hyperammonemic encephalopathy

Cranial magnetic resonance imaging was performed in three cases of acute hyperammonemic encephalopathy with three diverse etiologies: infantile citrullinemia, acute hepatic encephalopathy, and proximal urea cycle disorder. All three patients exhibited diffuse extensive cortical signal changes and swelling. Neurologic outcome was poor in all three cases. Knowledge of the magnetic resonance imaging findings of hyperammonemic encephalopathy may help in early diagnosis and treatment and could influence the neurologic outcome.

MRI findings in an adolescent with type I citrullinaemia

Citrullinaemia is a rare inborn error of urea cycle metabolism. We describe the MRI findings in a 16-year-old boy with type I citrullinaemia during an episode of acute hyperammonaemic encephalopathy and compare them to his previous follow-up MRI studies. MRI revealed bilateral high signal intensity in the cingulate, perirolandic, parietal and temporoinsular cortex, the subcortical white matter and left thalamus. Diffusion-weighted imaging showed high signal intensity and low apparent diffusion coefficient values in the frontoparietal lobes. To our knowledge, MRI findings in an adolescent with type I citrullinaemia have not been previously reported. Since our patient's neuroradiological findings showed greater similarity to type II citrullinaemia, we think his brain injury during this acute episode was probably age-related and independent of the type of citrullinaemia.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

Homozygous SLC25A13 Mutation in a Taiwanese Patient with Adult-onset Citrullinemia Complicated with Steatosis and Hepatocellular Carcinoma

Citrullinemia is a metabolic disorder characterized by elevated plasma concentrations of citrulline and ammonia. Adult-onset citrullinemia (type II, CTLN2) has been attributed to citrin deficiency caused by mutations in the SLC25A13 gene. CTLN2 is associated with a high incidence of hepatocellular carcinoma (HCC) in Japanese. We report a 48-year-old Taiwanese man with citrullinemia, who was in good health until the age of 34 when he had repeated episodes of consciousness disturbance. Hyperammonia (201 micromol/L) was found during an episode of coma. Liver function and electrolyte levels were normal at that time. Serologic markers of viral hepatitis B and C were negative. Analysis of genomic DNA extracted from peripheral blood leukocytes showed homozygous 851del4 mutation in exon 9 of the SLC25A13 gene on chromosome 7q21.3. Fourteen years after disease onset, at the age of 48, he was admitted due to an episode of coma. Abdominal sonography and computed tomography showed a 2.5 cm tumor in the left lobe of the liver, without evidence of liver cirrhosis. Wedge resection of the tumor was performed and grade 2 HCC was diagnosed. The nontumor part of the resected specimen showed chronic persistent hepatitis with moderate steatosis. The results in this case support that both citrin deficiency and steatohepatitis may contribute to hepatocarcinogenesis.

A neuroimaging approach to inborn errors of metabolism

There are numerous neurodegenerative and neurometabolic disorders of childhood. Individually, however, they are quite rare. Some may be seen only once in a lifetime at a given medical center, even one devoted to the specialized care of children. This article presents the classic neuroimaging features of some of the more commonly seen entities and of some of the more recently described metabolic disorders.

Comparison of clinical, magnetic resonance and evoked potentials data in a case of valproic-acid-related hyperammonemic coma

Magnetic resonance (MR) multimodality evoked potentials (MEPs) and clinical findings were correlated in a 47-year-old epileptic man in whom parenteral valproic acid (VPA) therapy induced severe comatose hyperammonemic encephalopathy without biological signs of hepatotoxicity (or hepatocytic dysfunction). Although the plasma VPA level remained within a normal therapeutic range, the ammoniemia increased to a toxic peak level at 411 micromol/l 24 h after symptom onset, requiring VPA therapy discontinuation. Brain MR monitoring demonstrated early cytotoxic edema evolving into delayed vasogenic edema and final brain atrophy. Concomitantly to abnormalities within the brainstem on MR images, an increase in brainstem conduction at MEPs and clinical disturbance of brainstem reflexes were observed at the initial phase of the disease course. Later, the resolution of the MR and MEPs abnormalities paralleled the clinical recovery of the reflexes.

Magnetic resonance imaging in late-onset ornithine transcarbamylase deficiency

We examined brain magnetic resonance imaging (MRI) in a cohort of seven patients with ornithine transcarbamylase deficiency (OTCD), and correlated MRI findings with clinical manifestations. Seven patients with OTCD, aged 3-27 years, all with a missense mutation, were involved in the study. We classified the OTCD patients clinically into four stages. MR study was performed with a 1.5-T superconducting magnet during asymptomatic periods. MRI revealed white matter lesions in two patients with an advanced clinical stage, i.e. T1 and T2 prolongated round lesions in the deep white matter and posterolateral angle of the lateral ventricle in one patient; small foci of T2 and T1 prolongation in the subcortical white matter in another. Parenchymal lesions, and cerebral and cerebellar atrophy were not found in the other five patients. MRI might be normal in the early stage of the disease, and progress in proportion to the clinical stage of OTCD. OTCD should be considered as a differential diagnosis of small foci in the white matter in children.