DIRA, DITRA, and new insights into pathways of skin inflammation: what's in a name?

Dermatology has a long-standing affinity for acronyms. From AGEP (acute generalized exanthematous pustulosis) to XP (xeroderma pigmentosum), acronyms have become a part of our dermatology lexicon, perhaps occasionally to the consternation of our colleagues in other specialties. In this issue, Brau-Javier et al1 describe a patient with a severe pustular skin disease called “DIRA”—an acronym for “deficiency of the interleukin 1 (IL-1) receptor antagonist,” which we first described in 9 pediatric patients in 2009.2 As its name suggests, DIRA is a new autoinflammatory disease linked to activation of the IL-1 pathway (Figure), joining the ranks of other IL-1–associated conditions with a prominent dermatologic component, foremost the cryopyrin-associated periodic fever syndromes (CAPS)—familial cold–induced autoinflammatory syndrome (FCAS), Muckle-Wells syndrome, and neonatal-onset multisystem inflammatory disease (NOMID). 3 Figure The pathogenesis of DIRA (deficiency of the interleukin 1 [IL-1] receptor [IL-1R] antagonist) and DITRA (deficiency of the IL-36 receptor [IL-36R] antagonist). Loss of the IL-1R antagonist leads to unopposed proinflammatory signaling by IL-1α . CAPS is caused by gain of function mutations that lead to oversecretion of the well-established fever causing cytokine IL-1Β, and all 3 disorders manifest in the skin as neutrophilic urticaria. In contrast, DIRA presents in the neonatal period with a severe neutrophilic “pustular” skin eruption, skin pathergy, and nail dystrophy, as well as elevated acute-phase reactants, sterile osteomyelitis, and periostitis. DIRA is caused by loss of function of the IL-1 receptor (IL-1R) antagonist, the first endogenous cytokine receptor antagonist identified that blocks IL-1 signaling (Figure). Absence of the IL-1R antagonist results in unopposed proinflammatory signaling via the cytokines IL-1α and IL-1β on the IL-1R type I (IL-1R1). DIRA is a rare condition that you may never encounter in your practice, so why bother filing away another acronym in the deep recesses of your dermatologic cortex? First, as Brau-Javier et al1 demonstrate, just as with CAPS, DIRA is exquisitely responsive to IL-1 blockade. Responses are similar to those seen following anti–IL-1 treatment for NOMID, the most severe form of CAPS; children who have been ill since infancy now feel well for the first time; others confined to wheelchairs because of disabling joint pain are able to walk; and growth curves begin to arc upward again for the first time in years. Interleukin 1–blocking therapy is now the standard of care for CAPS, and 3 Food and Drug Administration–approved agents, anakinra, rilonacept, and canakinumab, are currently available that provide targeted inhibition of IL-1 signaling.4 Second, understanding DIRA may yield new insights into the mechanism of other challenging pustular skin conditions. The cutaneous and systemic features of DIRA bear similarity to features seen in pustular psoriasis and SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, and osteitis), suggesting that IL-1 signaling may play a role in these conditions as well.