Burns (1984), 10, 372-373 Printed in Great Britain

Non-myocard ia l source of C K - M B in a pat ient w i th electr ical burn injury

A m i n A . N a n j i a n d J . D o u g l a s F i l i p e n k o

Divis ion o f Cl inical Chemistry, Vancouver General Hosp i ta l and Depar tment o f Pathology, Universi ty o f Bri t ish Columbia, Vancouver, Canada

HUMAN tissues conta in three forms of creat ine kinase (CK): these are dimers of the muscle and brain specific monomers , M and B, in the com- binat ions M M , MB and BB (Dawson et al., 1976). The diagnostic utility of measur ing C K - M B in sera of pat ients with myocardial infarct ion is well established (Rober t s and Sobel, 1978; Wagner , 1980). However, an increased serum C K - M B has been found in a n u m b e r of clinical condi t ions not associated with cardiac muscle damage (Nanji , 1983). We present here a pat ient who had elevated levels of C K MB associated with an electrical bu rn injury. There was no clinical, electrocardio- graphic or radiologic evidence of myocardial damage in this patient .

CASE REPORT A 47-year-old man sustained electrical injury when a pipe he was carrying contacted a crane cable which in

turn was resting against a high voltage power line carrying an estimated 66000 volts. He did not lose consciousness and his pulse was full and regular when he was examined by paramedical personnel. On admission to hospital, he was noted to have extensive burns to his hands, forearms and toes bilaterally. Pulse was 75 per min; regular, blood pressure 130/60 mmHg. The remain- der of the physical examination was normal. Relevant laboratory parameters included normal values for serum electrolytes, calcium, phosphorus, urea nitrogen and creatinine. Urine myoglobin was positive. Serial measu- rements of creatine kinase, lactic dehydrogenase, as- partate aminotransferase and CK MB are given in Table L CK isoenzyme determinations were carried out by electrophoresis on agarose gel followed by fluorescence scanning for quantitation (Helena Laboratories, Beaumont, Texas). There is no cross reactivity between CK-MM and CK MB in this procedure.

The patient was initially treated with fluids and diure- tics. A fasciotomy of his left and right hand was performed the day after admission.

Table I. Serial measurements of total creatine kinase (CK), isoenzymes MM (skeletal muscle) and MB (cardiac) lactic dehydrogenase (LDH) and aspartate aminotransferase (AST) in the patient

Days after Total CK (U/I) % MB admission (n = 25-232) % MM (n = 0-4) LDH (U/I)* AST (U/I)

0 47130 91.9 8.1 1843 996 40 000 92.6 7.4 1800 920

1 38 439 95-6 4.4 1 750 750 2 8000 97 3 791 612 3 8000 95 5 408 552 4 6420 100 0 339 400

* Isoenzyme analysis of all serum specimens showed the major isoenzyme present to be LDH 5 which is consistent with skeletal muscle damage. There was no LDH 1/2 'flip' indicative of myocardial damage. n = normal range.

Nanji and Filipenko: Non-myocardial source of CK-MB 373

Sequential daily electrocardiograms showed no evidence of myocardial damage. A 99technetium pyro- phosphate scan revealed only skeletal muscle necrosis and no evidence of myocardial damage. Furthermore there was no change in the lactate dehydrogenase pattern that would indicate myocardial damage. Two months later, the patient had a normal ECG tracing.

DISCUSSION The mos t severe cardiac effects tha t occur at the t ime of electrical injury are ventr icular fibrillation and myocardia l damage (Baxter, 1970). Since CK MB arises mainly f rom the myocard ium, it is likely tha t its presence in increased amount s could lead to an er roneous in terpre ta t ion of the presence of cardiac muscle damage. The mos t likely source of the C K - M B is skeletal muscle and increased amount s of C K - M B have been reported in as- sociat ion with rhabdomyolys is due to o ther causes (Seigel et al., 1980; Lot t et al., 1980).

The above pat ient demons t ra tes tha t an elevated level of C K - M B is no t a reliable marke r of the presence of myocardial damage in a pa t ient with electrical bu rn injury.

REFERENCES Baxter C. R. (1970) Present concepts in the management

of major electrical injury. Surg. Clin. North Am. 50, 1401.

Dawson D. M., Eppenberger H. M. and Kaplan N. O. (1976) Creatine kinase: evidence for a dimeric structure. Biochem. Biophys. Res. Commun. 21, 346.

Lott J. A., Spercher C. E. and Ayers L. W. (1980) Typhoid fever toxemia associated with destruction of skeletal muscle. Clin. Chem. 26, 1361.

Nanji A. A. (1983) Creatine kinase isoenzymes--a review. Musch, Nerve 6, 1983.

Roberts R. and Sobel B. E. (1978) Creatine kinase isoenzymes in the assessment of heart disease. Am. Heart J. 95, 521.

Seigel A. J., Silverman L. M. and Holman B. L. (1980) Peripheral source of MB band of creatine kinase in alcoholic rhabdomyolysis. J.A.M.A. 244, 580.

Wagner G. S. (1980) Optimal use of serum enzyme levels in the diagnosis of acute myocardial infarction. Arch Intern. Med. 140, 317.

Paper accepted in modified form 2 January 1984.

Correspondence shouM be addressed to: Dr Amin A. Nanji, Division of Clinical Chemistry, Vancouver General Hospital, Vancouver, Canada V5Z IM9.