Volume 184 - Issue 6
Erythema induratum: a case of mistaken identity
Author: James B Muir
Med J Aust 2006; 184 (6): 306-307. || doi: 10.5694/j.1326-5377.2006.tb00246.x
Published online: 20 March 2006
Published online: 20 March 2006
To the Editor: One of the Journal’s recent Lessons from Practice illustrates common errors in the approach to dermatological conditions.1 As in all areas of medicine, an accurate diagnosis is crucial to the management of any skin disease. This is especially so if a medical practitioner institutes treatments, such as oral steroids, that have considerable potential for causing morbidity. The lessons I would draw from the case of erythema induratum described are as follows.
If you suspect an unusual presentation of a common condition, perform investigations to confirm your suspicions. Although erythema nodosum classically occurs on the anterior lower leg, lesions above the knee may occasionally be seen.
To make a diagnosis, investigations need to be appropriate. The battery of blood tests ordered in the case described would not have shed light on the pathological process occurring in the skin. There is a reluctance among the general medical community to perform skin biopsies. These procedures cause little morbidity, have a high diagnostic yield, and should be within the skill set of any medical graduate. Concern over causing a scar is often cited as a reason for not doing a biopsy. But, in my experience, patients are rarely worried about such a prospect. Missing the diagnosis is surely of much greater concern. Taking a simple biopsy, including fat, at the initial presentation would have saved the patient in question a lot of trouble and risk.
If there is no response to your treatment, it may well be that the initial diagnosis was incorrect. For example, it is common to see “steroid-resistant eczema” that is actually intraepidermal carcinoma. Erythema nodosum will usually show at least some response to non-steroidal anti-inflammatory treatment. Lack of response to a treatment that usually works should lead to a re-evaluation of the diagnosis.
Systemic steroids should not be used for a dermatological condition without a firm diagnosis. Firstly, they can suppress many of the clinical and histological changes that allow a diagnosis to be made. Appropriate investigations need to be done before starting steroids. Secondly, a drug like prednisolone may well make matters worse, especially if, as here, there is an infectious aetiology.
Patients from areas in which tuberculosis is endemic should have this condition excluded before being given systemic steroids. A lack of obvious exposure to or symptoms of tuberculosis is not unusual in patients from such areas who are subsequently shown to harbour this infection.
The authors state that, as erythema induratum can resolve with corticosteroid treatment, this can lead to an erroneous diagnosis of erythema nodosum. Using response to treatment as a quasi-diagnostic test is dangerous indeed. Steroids will cause many conditions associated with significant inflammation to improve or even appear to resolve. But this does not mean that there is no infectious or malignant aetiology.
References
- Chew GY, Henderson C, Quin JW. Erythema induratum: a case of mistaken identity. Med J Aust 2005; 183: 534. 0_CEBFCHFH