Iatrogenic heavy metal intoxication due to prosthetic abrasion is rare but can mimic multisystemic degenerative diseases, especially mitochondriopathies. To our knowledge, one case with similar symptoms has been reported previously [
2] even though the symptomatic might be quite variable as reviewed by Gessner and colleagues [
3]. In the series of 25 cases, symptoms were diverse and included beside hip (84%) the involvement of further systems like cardiovascular (60%), audiovestibular (52%), peripheral motor-sensory (48%), or the thyroid (48%)as most frequent affection. Also, psychological functioning (32%), visual impairment (32%), and hematological, oncological, or immune affection (20%) occurred. In this review [
3], the mean cobalt levels were three times as high as in our patient and correlated well with symptom severity (r = 0.81,
p > 0.001), but symptoms occurred with cobalt levels as low as 20 μg/l. Cobalt is cytotoxic to neural cells, which explains the peripheral neuropathy, including damage to our patient’s optic and acoustic nerves [
4]. Cobalt ions destroy axonal mitochondria leading to axonal degeneration, including the optic nerve in rats [
5]. Chromium has also been attributed to neurotoxicity [
6], especially in cell- or animal models (fruit fly [
7], zebrafish [
8], and rat [
9]), but in humans, symptoms are rather limited to hemotoxic and carcinogenic effects.
Prosthetic abrasion can be caused by ceramic shrapnel or splitter when failed ceramic prostheses are replaced by metal-on-metal prostheses. In non-failed metal-on-metal prostheses, increased cobalt levels (> 7 μg/l) have been measured in two thirds of the recruited sample of (
n = 98) by Lodge and collegues [
10]. In cases with cobalt levels > 7 μg/l subclinical cardiac abnormalities have been described [
10]; we are not aware if studies focusing on neurological symptoms or subclinical neurological findings. In our case, no cobalt lowering therapy was initiated. There are some management suggestions with currently limited evidence as nicely discussed by Devlin and colleagues [
11] of previously published reports of single cases, including EDTA treatment and 2,3-dimercaptopropane1-sulfonate (unithiol). Both cases had cobalt levels of > 500 μg/l, almost eight times the levels of our patient.
Since hip replacement is common and mitochondriopathies rare, it seems advisable to consider testing for heavy metal toxicity in the differential diagnostics of multisystemic disorders mimicking mitochondrial diseases.