39 Dermatomyositis

Dermatomyositis

Anthony G. Ryan and Peter L. Munk

Clinical Presentation

A 65-year-old woman presented to her family practitioner with a recurrent history of progressive weakness, having particular difficulty climbing stairs. On examination, the patient had a striking violaceous discoloration and puffiness around her eyes and erythematous raised plaques on the skin overlying her knuckles. The practitioner noticed that the patient labored over standing up from the chair to get on the examination couch.

Figures 39A

Figures 39B

Figure 39C

Radiologic Findings

Conventional radiographs of the feet (Fig. 39A), right ankle (Fig. 39B), and distal foreleg (Fig. 39C) demonstrate sheets and conglomerations of calcification within the subcutaneous soft tissues, some of which assume the configuration of underlying tendons and musculature.

Diagnosis

Dermatomyositis.

Differential Diagnosis

Soft-tissue calcifications

METASTATIC

High calcium/phosphate
Hyperparathyroidism/renal osteodystrophy
Hypo- and pseudohypoparathyroidism

CALCINOSIS (NORMAL CALCIUM)

Dermatomyositis (universalis/circumscripta)
Scleroderma/CREST (calcinosis, Raynaud’s phenomenon, esophageal dysmotility, scleroderma, telangiectasia)
Idiopathic tumoral calcinosis (hyperphosphatemic)

DYSTROPHIC

Calcifications in soft tissues without metabolic disorder

The differential for sheets of calcification within the soft tissues is essentially limited to two entities:

Congenital myositis ossificans progressiva
Dermatomyositis

Discussion

Background

Thought of as an idiopathic autoimmune condition affecting the skin and skeletal muscle, dermatomyositis may also affect cardiac muscle, joints, and lungs. It is a rare condition, with only five new cases per million expected per year. It has a bimodal age distribution affecting children (5–14 years) and older middle-aged adults (45–65 years), women twice as often as men. In the childhood group, subcutaneous calcifications and necrotizing vasculitis tend to predominate, whereas in the older age group, there is a well-established association with solid tumors (especially of the stomach, colon, and lung), the risk being 4.4 times that of an age-controlled group. This approximates to 1 in 10 patients with dermatomyositis having an underlying malignancy. The diagnosis of dermatomyositis in a person over 40 should prompt a search for an occult malignancy. Surveillance is also suggested, as the malignancies may take up to 5 years to declare themselves.

Dermatomyositis rarely may be associated with other connective tissue disorders, for example, mixed connective tissue disorder and scleroderma.

Etiology

This is an autoimmune cell-mediated myopathy. The immune component is postulated to have an infectious origin, with protozoa (Toxoplasma gondii) and viruses (Coxsackie B RNA has been isolated from muscle biopsy specimens in one study in as many as 50% of dermatomyositis patients) under investigation.

Pathophysiology

Cytotoxic T cells dominate the cellular inflammatory response; however, a humoral contribution is also evident. Microvasculature changes include deposits of immune complexes in vessel walls and the presence of microtubuloreticular structures in endothelial cells consistent with an accompanying vasculitis.