Hand-wringing over the histology of mechanic’s hands and other cutaneous manifestations of dermatomyositis

By Warren R. Heymann, MD
April 23, 2018

Of all the cutaneous manifestations of dermatomyositis (DM) — the heliotrope rash, Gottron’s papules, Gottron’s sign, shawl sign, holster sign, flagellate erythema, photosensitivity, poikiloderma, periungual erythema, periungual telangiectasis, Samitz sign, pruritic erythema of the scalp, and panniculitis — none has perplexed me more than mechanic’s hands (MH).

MH was first described by Stahl et al in 1979 who noted the following: “A distinctive cutaneous lesion was seen on the hands of eight patients with connective tissue diseases; the lesions appear to be associated with an inflammatory myopathy. A nonpruritic hyperkeratotic eruption was accompanied by scaling, fissuring, and hyperpigmentation, giving the appearance of the calloused hands of a manual laborer.” The lesions were noted bilaterally on the ulnar aspect of the thumbs and radial aspects of the other fingers, mostly the index and middle finger, occasionally involving the palm. All patients had bilateral symmetrical proximal muscle weakness and evidence of an inflammatory myopathy on muscle biopsy. Four of the 8 were diagnosed with mixed connective tissue disease, 3 dermatomyositis, and 1 systemic lupus erythematosus. (1)

I tip my hat to Stahl et al. Looking at the images, I would have written these findings off as hand eczema, without a second thought. (Perhaps I am still doing that unwittingly.) Other cases that may be easier to recognize look more like Gottron’s papules located on the lateral aspects of the digits.

Over the years, MH has become commonly recognized as a clinical marker for pulmonary disease in the antisynthetase syndrome (ASS), defined as interstitial pneumonitis, polyarthritis, inflammatory myopathy and the presence of antisynthetase antibodies. Despite this association, there is a debate in the literature about the relationship between mechanic’s hands and DM. In their outstanding review of MH of 34 original studies, 23 case series/reports, and 7 literature reviews, Concha et al conclude that MH may be considered a characteristic feature of DM, based on clinical-pathologic correlation, despite the spectrum of definitions and disease associations in the literature. The authors (and other experts) are currently developing standardized classification criteria for MH using the Delphi technique. (2)

In a histological review of 40 patients with DM (yielding 45 biopsy specimens), Smith et al found the following: “perivascular inflammation (93%), vacuolar changes at the dermal-epidermal junction (80%), increased dermal mucin (61%), telangiectasias (53%), compact/hyperkeratotic stratum corneal layer (53%), epidermal atrophy (32%), follicular plugging (31%), and basement membrane thickening (16%). Colloidal iron and PAS stains revealed increased dermal mucin in 97% of biopsy specimens and basement membrane thickening in 61% of biopsy specimens. Of note, biopsies without vacuolar changes at the dermal-epidermal junction always showed an increase in dermal mucin. Follicular plugging could only be accurately assessed in 26 of the 45 biopsy specimens. The degree of inflammation was mild in 58% of biopsy specimens and moderate in 29% of biopsy specimens.” The authors also observed that the number of dyskeratotic keratinocytes correlated with the degree of vacuolar/interface changes at the dermal-epidermal junction. (3). MH were not specifically biopsied in this study.

It may be virtually impossible to distinguish DM from lupus histologically. The key, of course, that in connective tissue disease vacuolar alteration at the epidermal-dermal junction is crucial, however in approximately 20% of cases, it may not be present.

Ito et al evaluated the histopathology of MH in 6 patients with DM comparing it with the histopathology of 27 patients with palmoplantar eczema. Hyperkeratosis, basal vacuolar change and necrotic keratinocytes were seen in all cases of MH. Basal vacuolar change was not observed in any cases of palmoplantar eczema. Three cases of MH demonstrated a characteristic finding, a pseudocheckerboard pattern, in the hyperkeratotic horny layer; there were areas of alternating parakeratosis and orthokeratosis in a vertical arrangement alternating with the completely orthokeratotic areas in a horizontal arrangement. Although the same pattern was observed in 4 patients with palmoplantar eczema, those patients did not demonstrate any vacuolar alteration. The authors concluded that the ‘pseudocheckerboard pattern’ was not specific but may be a possible diagnostic clue for mechanic’s hands. (4)

Any mention of a checkerboard pattern of parakeratosis to a dermatopathologist will bring pityriasis rubra pilaris (PRP) to mind; therefore, we cannot forget about the Wong-type DM, which has PRP-like clinical features. Histologically, tiers of dyskeratotic cells (“columnar dyskeratosis” or “pseudocornoid” lamellae), reminiscent of porokeratosis, have been described in the Wong variant (4) (See “Waiting for Wong”, DI&I October 6, 2016)

Aside from MH, there have been two new important histologic studies related to DM.

Levy at al, reported the case of a 30 year-old woman with DM with psoriasiform lesions, (possibly potentiated by adalimumab) histologically demonstrating confluent parakeratosis, dermal edema, and mucin, accompanied by subtle vacuolar alteration. A biopsy from her finger displayed “columnar dyskeratosis” – the patient was not categorized as having the Wong variant, based on the absence of an erythroderma. (5)

In a study of 18 patients with DM panniculitis, Santos-Briz et al described a lobular panniculitis with lymphocytes as the main component of the infiltrate. Most cases displayed numerous plasma cells and lymphocytes surrounding necrotic adipocytes (rimming). Lymphocytic vasculitis and abundant mucin were also frequent findings. Late-stage lesions showed hyaline necrosis of the fat lobule and calcification. Immunohistochemistry demonstrated that most lymphocytes of the infiltrate were T-helper lymphocytes, with some B-lymphocytes in the lymphoid aggregates and small clusters of CD-123-positive plasmacytoid dendritic cells in the involved fat lobule. The authors concluded that the histology of DM panniculitis is identical to lupus panniculitis, necessitating clinical-pathologic correlation for a precise diagnosis. (6)

Whether it is MH, or other cutaneous features, you may be wringing your hands over trying to secure a diagnosis of DM; clinical-pathologic correlation is essential. My advice is to rely more on the clinical than the pathologic.

1. Stahl NI, et al. A cutaneous lesion associated with myositis. Ann Intern Med 1979; 91: 577-9.
2. Concha JSS, et al. Re-examining mechanic’s hand as a characteristic skin finding in dermatomyositis. J Am Acad Dermatol 2018; 78: 769-75.
3. Smith ES, et al. Dermatomyositis: A clinicopathological study of 40 patients. Am J Dermatopathol 2009; 31: 61-7.
4. Ito A, et al. Pseudocheckerboard pattern: An interesting histopathological finding in mechanic’s hands. J Cutan Pathol 2016; 43: 5-11.
5. Umanoff N, et al. Wong-type dermatomyositis showing porokeratosis-like changes (columnar dyskeratosis): A case report and review of the literature. Dermatopathology (Basel) 2015; 2: 1-8
6. Levy L, et al. Dermatomyositis: Histopathologic findings of parakeratosis and dermal edema revisited. J Cutan Pathol 2018; 45: 282-5.
7. Santos-Briz A, et al. Dermatomyositis panniculitis: A clinicopathological and immunohistochemical study of 18 cases. J Eur Acad Dermatol Venereol 2018. Mar 10 [Epub ahead of print]

---