Dermatomyositis in Patients with Darker Skin

00:01 Welcome to our lecture on dermatomyositis.

00:05 It is an idiopathic immune mediated inflammatory myopathy that causes progressive, symmetric, proximal muscle weakness and characteristic cutaneous manifestations.

00:18 The incidence is 0.5 to 8.4 cases per million, female to male ratio is 2:1, and it has a bimodal age presentation: earlier on 5 to 15 years, and later on 45 t o 60 years.

00:40 The cause of dermatomyositis is unknown, but it is thought to be caused by microangiopathy that affects skin and muscle.

00:51 Genetic factors have also been implicated, and some environmental triggers, for example infections, medications, and UV light.

01:02 Some of the predisposing health conditions involve or include smoking, vitamin D deficiency and malignancy.

01:12 Clinically, dermatomyositis may present with a heliotrope rash.

01:16 This is an erythematous rash.

01:19 Not so conspicuous in black patients, around the upper eyelids and periorbital edema. They may also present with a shawl sign which is fixed redness, which is bright red in white patients.

01:34 And again not so conspicuous in black patients, affecting the back, shoulders, chest and neck.

01:42 Patients may also present with lesions on the hands and knees.

01:47 These are called Gorton's papules and they are symmetric, erythematous papules located on the dorsal metacarpophalangeal and interphalangeal joints. Facial erythema is another clinical presentation of dermatomyositis, and it tends to present in a butterfly pattern that looks like malar rash of lupus or rosacea. But again, we need to be careful because the erythema may not be that conspicuous in black patients, but in lighter skinned African patients or skin of color patients, one m ay still be able to appreciate the erythema.

02:24 But those who are darker, it may be very difficult to see, and it may present as dusky red or plum-like or lichenoid presentation.

02:36 Here you see the Gottron sign, which are erythematous macules or patches , often located on extensor surfaces.

02:46 Nail fold changes include periungual erythema, dilated capillary loops at the proximal nail fold.

02:54 These are quite clear and obvious if one uses the dermatoscope or a magnifying glass.

03:03 Calcinosis cutis with subcutaneous calcification is very common in children, and this can be seen clearly on the X-ray on the right hand side.

03:16 Musculoskeletal involvement includes muscle weakness, and this is symmetric and involves proximal muscles, the deltoids, the hip flexors, and neck flexors.

03:29 This is mainly noted when climbing stairs, brushing hair, or standing up from a seated position.

03:37 Most oftentimes, a nice question to ask the patient is whether they are able to comb their hair, and if they've got proximal myopathy, they will tell you that they struggle to comb their hair.

03:50 A muscle atrophy is also another presentation of dermatomyositis.

03:57 The complications can involve other organs and tissues, causing arthritis, cardiac arrhythmias, interstitial lung disease, and pulmonary arterial hypertension, which can later on cause cor pulmonale and cardiac failure. The diagnosis is made by doing some laboratory tests as listed on the slide, but more specific are CK, your muscle enzymes aldolase, AST and ALT.

04:29 The dermatomyositis-specific antibody testing involves screening for Anti-Jo-1 antibodies and Anti-Mi-2 antibodies.

04:41 Other extra investigations include an EMG, which is altered in about 90% of cases, and of course, a muscle biopsy and histopathology is also helpful to confirm the diagnosis of dermatomyositis.

05:00 One has to screen for malignancy as dermatomyositis can be a paraneoplastic manifestation of an underlying malignancy and the following cancers that are listed there are other malignancies that are usually associated with dermatomyositis.

05:21 Lung cancer being the most common association, particularly amongst males.

05:28 And in women, the thyroid cancer has a higher association with dermatomyositis clinical presentation. Below is the diagnostic criteria which was developed in 2017 and it has the highest sensitivity and specificity, so a combination of clinical lab and muscle biopsy criteria is used to calculate the probability of idiopathic inflammatory myopathies, including dermatomyositis.

05:56 So there's clinical criteria if you look on the left column and lab criteria and of course the muscle biopsy features.

06:05 So one clinical criteria, two lab criteria and three muscle biopsy features as you can see on the screen.

06:14 Each criteria is assigned a certain number of points.

06:18 If one gets a total score which is then computed and converted into probability.

06:24 So as you can see on the slide there, if it's less than 50%, it's not dermatomyositis.

06:31 If it's between 50 and 55%, it's possible dermatomyositis.

06:36 And between 59 and 90%, it's probable dermatomyositis.

06:41 And more than 90% is definitive of dermatomyositis.

06:46 The differential diagnosis of dermatomyositis includes systemic lupus erythematosus.

06:53 Because these two conditions can have similar clinical manifestations.

06:57 But the key differences in diagnostic criteria and lab tests helps us to differentiate between the two.

07:05 Polymyositis is another differential.

07:08 But what is unique about it is that typically, there is no skin involvement.

07:15 Inclusion body myositis is another important differential in dermatomyositis.

07:21 It's usually not prominent, and there are no prominent cutaneous manifestations. The management of dermatomyositis includes the following: systemic glucocorticoids, immunosuppressive drugs, IV immunoglobulin, and for recurrent or refractory disease, the following biologics and mycophenolate mofetil can be used.