Muscle carnitine deficiency in old age. Case report and therapeutic results

Case Study of an Elderly Patient With New Onset Weakness

ABSTRACT

We present a patient presented with new onset progressive proximal weakness. On examination noted to have proximal weakness on upper and lower limbs, with preserved reflexes, without sensory involvement. Blood work revealed to have elevated creatine kinase. On electromyography testing shows myopathic features and also noted to have myotonic discharges. Muscle biopsy was obtained next which showed many vacuolization, marked increase in all fat content noted. These findings led us to checking carnitine levels which were noted to be significantly reduced with elevated carnitine palmitoyltransferase levels. These findings highly suggestive of systemic carnitine deficiency. Secondary causes of systemic Carnitine deficiency not identified in this patient and presumed to have primary systemic carnitine deficiency. Patient improved on oral supplementation of L- Carnitine.

Primary carnitine deficiency: adult onset lipid storage myopathy with a mild clinical course

We studied two adult patients with myalgia and muscular fatigability during prolonged physical exercise. Serum creatine kinase was increased and muscle biopsy revealed a lipid storage myopathy affecting predominantly the type I fibres. Skeletal muscle carnitine content was reduced to 15% and 21% of the normal mean values, while serum carnitine levels were either normal or decreased. Four months of oral therapy with L-carnitine (3 g per day) resolved the clinical symptoms completely in both patients, and a subsequent muscle biopsy confirmed a marked reduction of lipid storage, along with increased muscle carnitine levels. The analysis of renal carnitine excretion and the exclusion of possible secondary carnitine deficiencies in both patients are compatible with mild defects of the carnitine transporter in one patient and of carnitine biosynthesis in the other. Since myalgia and muscular fatigue are frequent but unspecified complaints of otherwise clinically unremarkable adult patients, it is important to identify myopathies associated with primary carnitine deficiency because they may be amenable to treatment.

Age-dependent decrease of carnitine content in muscle of mice and humans

Carnitine deficiency associated with impairment of muscle function has been described in infants and young adults as a result of inherited or acquired disease but there are no reports on carnitine levels in healthy aging people. In this paper we show a marked reduction of carnitine and its derivatives in muscle, and of long-chain acyl carnitine in heart of 6-month-old mice, when compared to animals of 6 weeks of age. Analysis of muscle samples of healthy humans of different ages showed a drastic reduction of carnitine and acetyl carnitine in the older subjects with a strong reverse correlation between age and carnitine levels.