Acne Fulminans

Acne fulminans is a rare, sudden, severe ulcerative form of acne with fever, joint or bone pain, and systemic inflammation. It is regarded as a dermatological emergency because of systemic illness and scarring.

It mostly affects adolescent boys and young men, usually with a background of mild to moderate acne. It can be triggered by starting isotretinoin (particularly high doses), anabolic steroids or testosterone, and sometimes by infection.

Features include a leucocytosis, raised inflammatory markers and, in some, lytic bone lesions (most often of the sternoclavicular joint), erythema nodosum, hepatosplenomegaly and myalgia. Outcomes are good with early treatment, and scarring is the main long term problem.

Pathophysiology.

A hypersensitivity reaction to Cutibacterium acnes antigens, with immune complex deposition and activation of neutrophils, produces ulcerating lesions and systemic inflammation. Androgen driven sebum production contributes. Isotretinoin may unmask the reaction.

• Sudden onset of inflamed, tender nodules and plaques that ulcerate, become crusted and haemorrhagic, mostly on the chest and back, and sometimes the face.
• Fever, malaise, myalgia, arthralgia and weight loss.
• Bone pain and swelling with lytic lesions (sternoclavicular, long bones), hepatosplenomegaly and erythema nodosum in some.
• Scarring from ulceration if treatment is delayed.

Red flags.

• Fever with ulcerating acne after starting isotretinoin or androgens.
• Severe bone or joint pain with swelling.
• Raised inflammatory markers with leucocytosis.

• Clinical diagnosis from the combination of severe ulcerative acne and systemic features, after exclusion of infection.
• Full blood count (leucocytosis, anaemia), C-reactive protein, erythrocyte sedimentation rate, liver tests, urinalysis and blood cultures.
• Radiographs or bone scan for bone pain, to find lytic lesions.
• Skin swab for bacteria and culture, and tests for mycobacterial and fungal infection if the picture is atypical.
• Drug history including isotretinoin, anabolic steroids and testosterone.

Differential diagnosis. Acne conglobata, pyoderma gangrenosum, Gram negative folliculitis, deep fungal infection, mycobacterial infection, vasculitis, pityriasis lichenoides et varioliformis acuta, rheumatic disease and osteomyelitis.

• Stop isotretinoin, anabolic steroids and other triggers.
• Start oral prednisolone 0.5 to 1 mg/kg/day for 2 to 4 weeks as the first step, with gastric protection and bone protection as needed. Start isotretinoin only after systemic features settle.
• Introduce isotretinoin at 0.1 mg/kg/day after 4 weeks of prednisolone, increase slowly to 0.5 to 1 mg/kg/day to a cumulative dose of 120 to 150 mg/kg, and continue prednisolone for at least 4 weeks together with isotretinoin before tapering over several weeks.
• Isotretinoin precautions: reliable contraception in women of childbearing potential, monthly pregnancy tests, lipid and liver monitoring.
• Antibiotics (doxycycline 100 mg twice daily or azithromycin 500 mg three times weekly) are used when infection is suspected or as an adjunct. Stop doxycycline when isotretinoin starts.
• Analgesia with paracetamol 1 g every 4 to 6 hours (maximum 4 g daily) or ibuprofen 400 mg three times daily with food for bone and joint pain.
• Wound care with non-adherent dressings, and early scar treatment after control. Refer to rheumatology if bone lesions persist.

Monitoring. Review weekly at first, then every 2 to 4 weeks. Monitor blood count, inflammatory markers, glucose and blood pressure on steroids, and lipids and liver tests on isotretinoin.

Referral and escalation. Refer urgently to dermatology, with admission for severe systemic illness.

Special groups. Isotretinoin is contraindicated in pregnancy. Use bone protection and monitor growth in adolescents on prolonged steroids.