Response to: Can patch test sensitization with gold sodium thiosulfate be ruled out?—A case report

We read with interest and applaud the commitment to patient safety with which the authors present “Can patch test sensitization with gold sodium thiosulfate be ruled out? —A case report”. However, we have concerns about the presentation and conclusions of this report. First, it omits the timing of patch test readings and fails to report patch test grade according to ICDRG reading criteria. The authors do mention, in the discussion, that the patient has oral gold alloys; however, the presence of other implants, a history of jewellery use or avoidance, etc. are not reported. Additionally, we respectfully disagree with their conclusions. Patch test active sensitization is generally defined as a negative patch test result followed by a flare-up after 10 to 20 days, and then a positive reaction after 3 days at retesting. However, gold sodium thiosulfate (GST) is a well-described, specifically noted exception to the above definition. This normal delayed reaction pattern is well described, including in known GST-allergic subjects who are incapable of being actively sensitized. A late reaction to GST is a positive reaction to GST, not a “negative reaction followed by a flare”. The crescendo in patch test reaction may be explained not only by the booster effect, but also by increased serum gold levels resulting from the patient’s dental gold restorations, and/or gold intake from homeopathic remedies, liquids, and food—all of which may decrease the minimal elicitation threshold for gold patch test reactions. Finally, it must be mentioned that gold contact allergy frequently presents as facial dermatitis, even when clear relevance is not found. The patient presented with facial dermatitis, has ongoing gold exposure, and developed a positive reaction to GST in a time frame characteristic for patients with known gold allergy—this is consistent with gold allergic contact dermatitis (ACD) until proven otherwise. The clinical relevance—or lack thereof—can only be considered after removal of the known ongoing exposure: the dental gold. Consider the recent report of a woman complaining of facial and flexural dermatitis with known multiple dental alloys but no oral symptoms. She had positive patch test reactions to multiple metals— including gold. This woman’s cutaneous symptoms resolved completely after removal of amalgam-containing and gold-containing oral alloys. Although the authors seem to consider “subclinical” gold sensitization from oral exposure to be less plausible than active sensitization, prior investigations have found that this is exceedingly common—asymptomatic patients (ie, without stomatitis) with gold dental restorations have positive gold patch test reactions in up to 30% of cases. The authors seem concerned about the persistent nature of the original gold patch test reaction—and the case report implies that this persistent reaction is what prompted repeat patch testing. These persistent reactions are already well reported in the literature. They are common, and there is no known association between persistent reactions and active sensitization. The hypothesis that gold granulomas may cause active sensitization is interesting, but not supported by this case, as this patient had a positive gold patch test reaction concomitantly with granuloma formation, and is thus incapable of de novo or “repeat” sensitization. Tumour necrosis factor-α expression is seen in both granulomatous processes and ACD. Its presence is non-specific and does not support active sensitization by patch testing. As written, this case best represents a true gold-allergic patient, probably sensitized via oral gold exposure, with currently unclear but possible clinical relevance warranting investigation, and a characteristic persistent reaction.