MERS is a clinical-radiological syndrome with mild encephalitis/encephalopathy and the MRI finding of a transient lesion in SCC (type I MERS) or associated in other white matter areas (type II MERS). It has been reported that MERS is the second most common infectious encephalitis/encephalopathy syndrome in Japanese children .
The syndrome mainly affects children and young adults; the prognosis is favorable with complete or nearly complete neurological and radiological resolution within days or weeks. The exact pathophysiology is unknown. There are few reports in the literature on MRI findings of porphyria cases with central nervous systems (CNS) involvement[6, 7]. Many of studies suggested that MRI changes are related to posterior reversible encephalopathy syndrome (PRES)[8–10]. In this report, we have presented a new MRI finding of AIP,which had never been reported before.
According to Hoshino et al,the diagnostic criteria of MERS are the following: (1) Clinical onset associated with neuropsychiatric symptoms, such as impaired consciousness within 1 week after fever onset; (2) Complete recovery without sequelae, mostly within 10 days after the onset of neuropsychiatric symptoms; (3) High-signal- intensity lesion in the SCC; (4) Involvement of the entire corpus callosum and bilateral cerebral white matter with symmetrical pattern may also occur; (5) Lesion disappearing within 1 week, with no residual signal changes or atrophy. Despite our proband performed the second MRI 15 days after the first one, and without fever, she fulfills this diagnostic criterion. MERS is classified in MERS type I and MERS type II, depending on the involvement of SCC alone or also other white matter areas, our patient was a MERS type I case.
Acute intermittent porphyria (AIP) is one of four forms of acute porphyria that is caused by an inherited deficiency of PBGD, which catalyzes the third enzymatic step in the biosynthesis of heme. Symptoms in AIP, which occur as intermittent attacks and may be life-threatening, are caused by excess production of porphyrin precursors on the visceral, peripheral, autonomic, and central nervous systems. Clinical manifestations of CNS involvement include epileptic seizures, impaired consciousness, behavior changes and hyponatremia caused by inappropriate antidiuretic hormone syndrome[11, 12]. The symptoms of our proband included abdominal pain, nausea, vomiting, confusion, delirium, seizures and hyponatremia.
The reason for the transiently reduced diffusion within the lesions on MRI is still unknown, which has been suggested to be due to hypotonic hyponatremia or a myelin-specific neurotoxin released References by a pathogen[13, 14]. The possible cause of hyponatremia of MERS is SIADH, which is also considered as a cause of hyponatremia in patients with AIP. Since she had no evidence of infection, maybe hyponatremia as a contributing factor of MERS of our proband. However, urine and blood osmolality of our proband were both lower than normal, maybe because she had taken 0.25 mg tolvaptan 12 hours before, tolvaptan could significantly decrease the urine osmolality[15, 16]. Tolvaptan didn’t exacerbating symptoms in the acute phase of AIP of our proband, maybe it is safe to use of Tolvaptan in AIP with hyponatremia.
In mainland of China, the lab investigations (erythrocytic PBG deaminase levels, urinary, fecal, and plasma porphyrin levels) are unavailable, molecular genetic testing provides a precise diagnosis to differentiate AIP from other acute porphyrias, and then can be used to identify AIP in relatives of the proband. In this study, we identified a novel PBGD gene mutation (W198*) in a Chinese family. Almost all cases of MERS have occurred in children in East Asian populations, mostly Japan, there has also been one case report of sisters with MERS, which would support the genetic vulnerability hypothesis. Since AIP is a hereditary disease, suggesting a genetic factor might be involved in some MERS patients. This is the first reported case of MERS following AIP and she had a novel PBGD splicing mutation, our case report widens the phenotype of the neurological manifestations associated with AIP. Further clinical, radiological and genetic studies of MERS are necessary for a definite conclusion.