To the editor: A vascular mechanism responsible for renal damage during attacks  of  acute  intermittent  porphyria

(AIP), due to sustained  vasospasm, appears  to  exist.1 Hyponatremia  is  a common complication in this disease, that  is  usually  related  to  a  syndrome of  inappropriate  secretion of antidiuretic hormone (SIADH).2,3 Rhabdomyolysis may  be  a  frequent  complication  during  hyponatremia  correction in which elevation of creatine phosphokinase  (CPK)  levels  runs  parallel to  the  recovery of  sodium  levels  and renal  function  is  not  usually  impaired.



We report the case of a 16-year-old female patient born  in Mauritania, with a family  history  of  acute  intermittent

porphyria, who was admitted to hospital for abdominal pain and vomiting for the past several days associated to an impaired  consciousness  level  and  two  episodes of generalized tonic-clonic seizures, after which  she  remained  in  a  postictal state and required orotracheal intubation and mechanical  ventilation.  Laboratory test results include severe hyponatremia (Na  95 mM/L;  normal,  135-145)  associated to plasma (244 mOsm/L) and urinary hyposmolarity (222 mOsm/L), urinary  frequency  and  data  suggesting hypovolemia (central venous pressure of

4 mmHg).  Isotonic  saline  infusion was therefore  started.  Rhabdomyolysis  was detected 24 hours after admission. Maximum  CPK  levels  of  35628  U/L were found at 48 hours, but no renal function impairment  was  noted.  Patient  clinical signs  and  history  suggested  an AIP attack, that was confirmed by measuring in a spot urine sample  levels of deltaaminolevulinic acid of 39.7 mg/g (normal, 0-5), as well as values in 24-hour urine of 154.3 mg of porphobilinogen (normal,  0-2),  484  μg/24  h  of  coproporphyrin  (normal,  0-60),  and  1,471μg/24  h  of  uroporphyrin  (normal,  0- 22).  Once  diagnosis  was  confirmed, treatment was started with intravenous

human  hemin  at  3  mg/kg/day  for  4 days.  The  patient  developed  arterial hypertension  that required administration  of  beta-blockers.  Clinical  course was  satisfactory,  with  a  progressive improvement  in  consciousness  level. Mechanical ventilation was withdrawn 6  days  after  admission,  and  patient was  discharged  with  a  normal  consciousness  level  and  no  symptoms. A genetic  study  to  search  for mutations and screen for heterozygous family carriers was requested.



AIP is  the most  common  and  severe of hepatic porphyrias.4 Disease transmission  is  autosomal  dominant, and  the gene encoding AIP is located in the long arm of chromosome 11. AIP causes deficiency of the enzyme uroporphyrinogen I synthetase, formerly called porphobilinogen  synthetase  (PBG),  thereby  blocking  heme  synthesis.  The most  typical clinical  signs  include nausea, vomiting, constipation, diarrhea, urinary retention,

tachycardia, hypertension, mental symptoms,  and  muscle  pain  and  weakness. These attacks may be triggered by barbiturates,  anticonvulsants,  estrogens,  oral contraceptives,  alcohol,  or  low-calorie diets.  Seizures  may  occur  in  20%  of cases, particularly in patients with hyponatremia.



The relationship between hyponatremia  and  rhabdomyolysis  may  apparently result  from intracellular potassium efflux  to  compensate  for  the  cell edema caused by decreased sodium levels, which would  cause  a decrease  in transmembrane  potential  and  hence  in muscle metabolism.5 Other authors postulate that it is hyponatremia correction itself which  causes  changes  in muscle cells ion concentrations and osmolarity resulting  in  incapacity  to maintain  homeostasis  in  cell  volume  regulation. This  would  cause  membrane  fragility

and  muscle  enzyme  release  into  the bloodstream.6