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There are three dermatological conditions which, when viewed under the microscope, are characterized
by the presence of necrobiosis (degenerative collagen). These include granuloma annulare, rheumatoid
nodules, and necrobiosis lipoidica diabeticorum. These lesions can usually be differentiated on a
clinical basis. Normally, granuloma annulare appears as a predominately dermal (skin) lesion. The
rheumatoid nodule is a nodule (lump) arising in the subcutaneous tissue over the surfaces of the
fingers, elbows, knees, and toes. Necrobiosis lipoidica diabeticorum will show extensive atrophy
(loss of tissue substance) of the epidermis of the pretibial areas of a patient with diabetes.
While the clinical characteristics of these three lesions are quite distinctive, in some cases
there is a significant overlap.
Let's look at each of these lesions individually.
Granuloma Annulare
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These lesions are common in children as well as young adults. They are particularly common in
those individuals with a strong family history of diabetes mellitis. The initial granuloma
annulare lesion often resembles a mosquito bite and appears on the wrist, ankle, elbow, knee,
or the digit of a hand or foot. These lesions are asymptomatic and do not itch. A granuloma
annulare lesion gradually spreads peripherally in a circular pattern with no apparent scaling.
Ringworm or tinea corporis may often be the first diagnosis that comes to mind with these lesions.
However, there is no apparent scaling on which to do a KOH exam for the presence of fungi.
In the majority of cases there are only one or two lesions, but dozens of lesions could
develop. This is normally not a condition that should cause much concern for the patient
or parents. In most cases, it can be easily cleared with intralesional steroid therapy.
However, there are
occasions when this condition can occur extensively over the skin and intralesional steroid therapy becomes
inappropriate. Many forms of systemic therapy including PUVA therapy, dapsone, methyltrexate
and retinoid therapy can be effective in clearing these more severe lesions.
See the examples of Granuloma Annulare shown below.
Rheumatoid Nodules
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As you would expect by the name, these lesions normally occur in patients with rheumatoid arthritis.
The lesions are usually asymptomatic, and are most often located over the extensor surfaces of joints on the
hands, wrists, elbows, knees, ankles, and toes. They usually appear at some point over the course of
the disease and are not particularly responsive to the systemic therapy for rheumatoid arthritis.
However, they may be easily treated with intralesional cortiosteroids injections. Although this
technique is very effective, physicians may ignore these nodules as unsightly but
insignificant characteristics of the underlying disease.
Necrobiosis Lipoidica Diabeticorum
Clinically, this very distinctive lesion can occur on many parts of the body, but normally
it is seen on the pretibial (shin) area of the lower legs. It is generally tied to diabetes, and may appear
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before the onset of the diesaese, in its early stages, or long after it has become a problem. These lesions have
three distinct clinical characteristics. The first is significant atrophy or loss of
tissue substance. The growth of the lesion often results in the destruction of hair follicles and sebaceous glands.
The second characteristic is a thinning of the epidermis. Telangiectatic vessels (small bright red blood vessels)
may become visible, particularly around the periphery of the lesions. The third sign is a yellowish or orange color in the
central portion of the lesion caused by
lipid deposits. Necrobiosis lipoidica diabeticorum lesions
may become quite extensive and involve almost the entire cutaneous surface of the pretibial area. If left untreated,
they can become extensive ulcerated lesions which are extremely resistant to conventional therapy. Intralesional
steroid therapy in the early stages of this problem can be quite effective. However, as with any lesion
associated with diabetes, careful management of the blood glucose level is essential to create an
environment where this lesion can be effectively treated.
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