Epilepsy and porphyria: new perspectives

Neurology of the acute hepatic porphyrias

Porphyrias are a set of rare inherited metabolic disorders, each of them representing a defect in one of the eight enzymes in the haem biosynthetic pathway resulting in the accumulation of organic compounds called porphyrins. Acute hepatic porphyrias (AHP) are those in which the enzyme deficiency occurs in the liver, of which acute intermittent porphyria is by far the most common subtype. Neurology of the AHP is still challenging in practice, and patients rarely receive the correct diagnosis early in the disease course. For AHP, which primarily affects the central and peripheral nervous system, the cause of symptoms seems to be the increased production of neurotoxic precursors, in particular delta-aminolaevulinic acid and porphobilinogen. Neurological complications usually result from severe episodes of acute attacks. The neurologic hallmark of porphyrias is an acute predominantly motor axonal neuropathy resembling a Guillain-Barré syndrome that generally occurs after the onset of other clinical features such as abdominal pain and central nervous system manifestations. Neuropsychiatric syndromes, seizures, encephalopathy, and cerebrovascular disorders are among the possible central nervous system presentations. Therapeutic approach to AHP is divided into management and prophylaxis of an acute attack, including long standing options such as intravenous hematin and new therapeutic agents such as givosiran.

Nonconvulsive status epilepticus secondary to acute porphyria crisis

Both variegate and acute intermittent porphyria can manifest with various neurological symptoms. Although acute symptomatic seizures have been previously described, they are typically tonic–clonic and focal impaired awareness seizures. Convulsive status epilepticus and epilepsia partialis continua are rare and have been described on a case report basis. To our knowledge, there are no previously reported cases describing non-convulsive status epilepticus (NCSE) with electroencephalogram (EEG) documentation in the setting of acute porphyria crisis. We report a unique presentation of NCSE, which resolved after administering levetiracetam in a patient with variegate porphyria, without a known seizure disorder.

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Seizures among acute intermittent porphyria (AIP) patients are not uncommon with prevalence being as high as 10%–20%.

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Non-convulsive status epilepticus (NCSE) in variegate porphyria (VP) patients should be considered in patients with altered mental status and acute porphyric crisis.

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Recognition and avoidance of prophyrogenic anti-seizure medications is important in the treatment of these patients.

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Levetiracetam and hemin are potential treatment combinations for nonconvulsive status epilepticus in acute porphyria crisis patients.

Porphyria: often discussed but too often missed

The diagnosis of acute intermittent porphyria (AIP) is often overlooked. We describe a patient with this condition who had all the 'bells and whistles', in whom the diagnosis was only made after considerable delay. Far from an esoteric condition haunting examination candidates, AIP is an important cause of a broad spectrum of neurological symptoms. Its early recognition allows the astute clinician to prevent potentially devastating sequelae. We provide practical guidance on the investigation and management of this complex disorder. With a 'back to basics' approach to the underlying genetics and biochemistry, we hope to dispel some of the confusion that may obstruct a timely diagnosis.

Antiepileptic Drugs and Liver Disease

Acute, symptomatic seizures or epilepsy may complicate the course of hepatic disease. Choosing the most appropriate antiepileptic drug in this setting represents a difficult challenge, as most medications are metabolized by the liver. This article focuses on the acute and chronic treatment of seizures in patients with advanced liver disease and reviews the hepatotoxic potential of specific antiepileptic drugs. Newer antiepileptic drugs without, or with minimal, hepatic metabolism, such as levetiracetam, lacosamide, topiramate, gabapentin, and pregabalin should be used as first-line therapy. Medications undergoing extensive hepatic metabolism, such as valproic acid, phenytoin, and felbamate should be used as drugs of last resort. In special circumstances, as in patients affected by acute intermittent porphyria, exposure to most antiepileptic drugs could precipitate attacks. In this clinical scenario, bromides, levetiracetam, gabapentin, and vigabatrin constitute safe choices. For the treatment of status epilepticus, levetiracetam and lacosamide, available in intravenous preparations, are good second-line therapies after benzodiazepines fail to control seizures. Hepatotoxicity is also a rare and unexpected side effect of some antiepileptic drugs. Drugs such as valproic acid, phenytoin, and felbamate, have a well-recognized association with liver toxicity. Other antiepileptic drugs, including phenobarbital, benzodiazepines, ethosuximide, and the newer generations of antiepileptic drugs, have only rarely been linked to hepatotoxicity. Thus physicians should be mindful of the pharmacokinetic profile and the hepatotoxic potential of the different antiepileptic drugs available to treat patients affected by liver disease.

Bovine congenital erythropoietic protoporphyria in a crossbred limousin heifer in Ireland

An unusual case of an 11-month-old, black Limousin-cross heifer, with an 8-month history of episodic seizures and photosensitisation, was referred by a veterinary practitioner to the Farm Animal Section of the UCD Veterinary Hospital, School of Veterinary Medicine, University College Dublin, Ireland, in August 2014. Following an investigation, a diagnosis of Bovine Congenital Erythropoietic Protoporphyria (BCEPP) was made. To the authors’ knowledge this is the first report of such a case in Ireland. BCEPP should be considered as a differential diagnosis in young animals displaying periodic seizures and/or photosensitisation.

Acute intermittent porphyria: a diagnostic challenge

Acute intermittent porphyria is a metabolic disorder rarely seen in prepubertal children. A delay in diagnosis of acute intermittent porphyria is common because of variable and nonspecific symptoms. We report an 8-year-old boy with right hemimegalencephaly and intractable seizures, who presented with dark-colored urine, hypertension, increasing lethargy, fluctuating seizures, and poor oral intake. He subsequently developed hyponatremia secondary to syndrome of inappropriate antidiuretic hormone secretion. His urinalysis was negative for red blood cells, and a random urine porphobilinogen level was elevated. Further biochemical and molecular testing confirmed the diagnosis of acute intermittent porphyria. His antiepileptic medications were discontinued and hemin administered, with dramatic clinical improvement. The diagnosis of acute intermittent porphyria was challenging because of his underlying neurologic condition. This case highlights the variable presentation of acute intermittent porphyria and emphasizes the importance of considering the diagnosis even in young patients with underlying neurologic conditions when they present with nonspecific neurovisceral symptoms or with unexplained neurologic deterioration.

Various pharmacogenetic aspects of antiepileptic drug therapy: a review

Pharmacogenetics concerns the influence of an individual's genetic background on the pharmacokinetics and pharmacodynamics of xenobiotics. Much of the pharmacogenetic data in the field of epilepsy deals with the pharmacokinetics of antiepileptic drugs (AEDs). In particular, two polymorphisms of cytochrome P450 2C9 are known to slow down the metabolism of phenytoin to a degree that increases the risk of the neurotoxic adverse effects of this drug among carriers of these polymorphisms. A significant number of patients with epilepsy do not respond to AEDs and such pharmacoresistance is a major, largely unsolved, problem that is likely to be multifactorial in nature. In this regard, genetic factors may influence transmembrane drug transporter proteins, thereby modifying the intracerebral penetration of AEDs. Monogenic idiopathic epilepsies are rare and frequently associated with ion channel mutations; however, to date, a consistent relationship between changes in channel properties and clinical phenotype has not been established nor has any association between genotype and response to specific treatment options. Polymorphisms of drug targets may represent another genetic facet in epilepsy: a recent study demonstrated for the first time a polymorphism of a drug target (the alpha-subunit of a voltage-gated sodium channel) associated in clinical practice with differing response to two classic AEDs. Adverse drug reactions and teratogenicity of AEDs remain a major concern. Whole-genome single nucleotide polymorphism profiling might in the future help to determine genetic predisposing factors for adverse drug reactions. Recently, in Han Chinese treated with carbamazepine and presenting with Stevens-Johnson syndrome, a strong association was found with HLA B*1502. If genetically targeted drug development becomes more affordable/cost efficient in the near future, the development of new drugs for relatively rare diseases could become economically viable for the pharmaceutical industry. The synergy of lower trial costs and efficacy-based prescribing may reduce the cost of medical treatment for a particular disease. This hypothetical advantage of the practical use of pharmacogenetics is, however, counterbalanced by several possible dangers, including illicit data mining and the development of a human 'genetic underclass' with the risk of exclusion from, for example employment or health insurance, because of an 'unfavourable' genetic profile.

Diagnosing Epilepsy in the Elderly

Elderly individuals represent the fastest-growing segment of the US population. Seizures are common among elderly persons, and the etiology, clinical presentation, and prognosis of seizure disorders can often differ between elderly patients and younger individuals. However, published information regarding the diagnosis and management of epilepsy in elderly patients is scarce. Because a number of conditions that are common in elderly patients may resemble epilepsy, diagnosis can be challenging. Cardiovascular conditions, migraines, drug effects, infections, metabolic disturbances, sleep disorders, and psychiatric disorders are all associated with signs and symptoms that may often mimic epilepsy. New paradigms must be put into practice to establish an accurate diagnosis in the elderly patient; besides an initial evaluation, the patient history and an electroencephalogram should be obtained. Proper diagnosis is essential for proper treatment in the elderly patient.

Acute intermittent porphyria, Rasmussen encephalitis, or both?

A case of a young woman who suffers from refractory epilepsy in the form of Rasmussen encephalitis and acute intermittent porphyria is presented. The patient developed refractory partial seizures with progressive hemispheric atrophy in the first decade. Both her serum and cerebrospinal fluid contained significantly elevated levels of anti-GluR3B antibodies. Her serum also contained anti-NR2A antibodies (directed against the N-methyl-D-aspartate receptor). Seven years later, acute intermittent porphyria was diagnosed as she developed an acute episode of abdominal pain, dark urine, and hyponatremia. For several years, all attempts to discontinue porphyrinogenic antiepileptic drugs such as phenobarbital and valproate resulted in seizure worsening. During a major acute intermittent porphyria crisis, brain edema and coma developed, allowing the discontinuation of phenobarbital. On recovery, atrophy of the right hemisphere ensued. Several etiologic hypotheses are presented. Double insults, porphyria, and an autoimmune process are suggested for the development of Rasmussen encephalitis in this patient. The authors recommend testing for porphyria in cases of Rasmussen encephalitis and other intractable seizures.

Kortikale Amaurosis und Status epilepticus bei akuter Porphyrie

The most common neurologic manifestations of acute intermittent porphyria (AIP) are autonomic visceral neuropathy, peripheral motor neuropathy, and CNS dysfunctions including seizures and neuropsychiatric disturbances. In rare instances, however, AIP patients have presented with acute cortical blindness. We present a 20-year-old woman who suffered her first attack of AIP. Following 1 week of abdominal pain, she was transferred from a surgical department because of sudden visual loss and deterioration of consciousness. On admission, she developed several generalized seizures. Magnetic resonance imaging showed bilateral DWI lesions occipitally and in the left anterior circulation. Cerebrospinal fluid, MR angiography, and duplex ultrasound were normal. On the following day, sedation and intubation became necessary because of a generalized status epilepticus. Analysis of porphyrinogens in blood, urine and stool showed significantly elevated values. Intravenous therapy with häm-arginate was initiated and antiepileptic therapy was changed to gagabentine. Under this therapeutical regime she remained stable and extubation was possible 48 h later.

Crystal Structures of the PNA−Porphyrin Complex in the Presence and Absence of Lactose: Mapping the Conformational Changes on Lactose Binding, Interacting Surfaces, and Supramolecular Aggregations,

The extraordinary recognition specificity of lectins for carbohydrate ligands appears to be violated as they also bind to porphyrins and other noncarbohydrate ligands. In this study, crystal structures of meso-tetrasulfonatophenylporphyrin (H(2)TPPS) bound to peanut agglutinin (PNA) in the presence and absence of lactose were determined. The binding of H(2)TPPS with PNA involved 11 molecules of H(2)TPPS in different supramolecular stacking arrangements associated with a tetramer of PNA in the crystals of the PNA-H(2)TPPS binary complex as well as the PNA-H(2)TPPS-lactose ternary complex. The ternary complex involved lactose binding only to two subunits of the PNA tetramer, which did not have porphyrin interacting in the vicinity of the carbohydrate-binding site. Comparison of the two structures highlighted the plasticity of the carbohydrate-binding site expressed in terms of the conformational change in lactose binding. The unusual quaternary structure of PNA, which results in exposed protein-protein interaction sites, might be responsible for the porphyrin binding. The association of porphyrin in diverse oligomeric stacking arrangements observed in the PNA-H(2)TPPS complex suggested the possibility of protein-porphyrin aggregation under abnormal physiological conditions. The structures described here provide a possible native conformation of the carbohydrate-binding site of PNA in the absence of the ligand, highlight mapping of the unsaturated binding surfaces of PNA using porphyrin interactions, indicate new leads toward possible application of this lectin in photodynamic therapy, and exhibit diverse modes of porphyrin-lectin interactions with implications to porphyria, a disease that results from abnormal accumulation of porphyrins.

Effect of Antiepileptic Drugs on the Urinary Excretion of Porphyrins in Non-porphyric Subjects

The action of some anticonvulsant drugs as the causal agents of attacks of acute porphyria has been widely documented in the literature. However, little attention has been paid to the effect of these drugs on the urinary excretion of porphyrins in non-porphyric subjects. In a sample of 82 epileptic patients treated with phenobarbital (n = 54), phenytoin (n = 64), carbamazepine (n = 33), and valproate (n = 8), the daily doses were expressed according to a drug score that would reflect the capacity of these drugs as enzymatic inducers when administered in polytherapy. A significantly increased urinary excretion of D-glucaric acid (DGA) and porphyrins was found in this group of patients (P<0.001), with coproporphyrin being the major fraction in all cases (>60%). Urinary DGA had a highly significant correlation with the drug score (r = 0.783, P<0.001); however, no significant correlations were found between the urinary porphyrins and DGA (r = 0.005) or the drug score (r = 0.053). Neither was any significant relationship found between the urinary porphyrins and the serum activity of 5'-nucleotidase (r = 0.066) or the presence of a cholestasis objectivized through the presence of the isoform of gamma-glutamyltransferase with beta-globulins electrophoretic mobility. However, in a group of 10 patients a significant correlation was found between the urinary excretion of porphyrins and beta-N-acetylhexosaminidase (r = 0.790, P<0.01). Therefore, it does not appear that the liver enzyme induction, or even a subclinical cholestasis, produced by the antiepileptic drugs administered to these patients may serve to explain the increase in the urinary excretion of porphyrins. A possible renal origin is proposed for the increase of urinary porphyrins in these cases.