Contributed by David Lacomis, M.D.DIAGNOSTIC INTERPRETATION:
Myopathy with cytoplasmic bodies and multi-cores. These findings are most consistent with a congenital myopathy or ipecac (emetine) toxicity.
COMMENT:
A urine toxin screen for emetine (found in ipecac) was positive. The patient later admitted using ipecac for purging.
Initially, an inflammatory myopathy was the suspected cause of this patient's weakness and was the reason for the muscle biopsy. In retrospect, the acute onset of limb and oropharyngeal weakness (causing dysphagia with nasal regurgitation) is atypical for polymyositis which generally worsens over months. An infectious or parasitic myositis, toxic myopathy, or metabolic myopathy could present in this fashion.
The muscle histopathology reveals a striking constellation of findings, but no inflammatory infitrates. The major findings are cytoplasmic inclusions and multi-cores. The cyoplasmic inclusions are cytoid bodies which are thought to be related to or stem from Z-bands. They consist mainly of the thin filament actin or of intermediate filaments. They are a non-specific histopathologic finding that occurs in many myopathic disorders, but when present in large numbers in a young person, they raise the possibility of a congenital myopathy, called cytoplasmic body myopathy. In addition, the multicores (also called minicores) may occur in congenital myopathies, but they are also non-specific and of uncertain origin.
However, the abrupt onset of weakness and very high CK made a congenital myopathy exceedingly unlikely. The pathologic findings described above also occur in ipecac myopathy which usually occurs in patients with eating disorders. After review of the histopatholgy, the possibility of ipecac myopathy was raised in this patient with anorexia nervosa, and the urine toxicolgic screen was performed. The patient later admitted to abusing ipecac.
Ipecac contains the alkaloid emetine which is a skeletal and cardiac muscle toxin when ingested chronically. The myopathy is reversible upon discontinuation of the drug. In addition to limb weakness, myalgias, elevation in CK, and myopathic EMG changes are common elements of ipecac myopathy. Histopathologic studies in humans disclosed a non-inflammatory myopathy with cores, multi-cores, and usually cytoplasmic bodies as noted in our patient.
The specific cause of emetine myotoxicity is uncertain. Emetine does inhibit mitochondrial oxidative phosphorylation, but studies of mitochondrial oxidation in animal models have not disclosed a primary mitochondrial disturbance in muscle. In one patient with ipecac myopathy, mitochondrial respiratory chain enzymes were normal, but carnitine levels were reduced in skeletal muscle. The reason for the reduction in carnitine in that single patient is unknown. In addition to altering mitochondrial function, emetine inhibits protein synthesis. Given the alterations in myofilaments described in patients with ipecac myopathy, it is most tempting to speculate that weakness is due to direct effects of emetine on myofilament proteins.
Following discontinuation of ipecac use, this patient reported a return of muscle strength.
REFERENCES
Contributed by David Lacomis, M.D.
