What systemic diseases and conditions are most commonly associated with pyoderma gangrenosum, and what are the typical demographic characteristics?

Pyoderma Gangrenosum: Systemic Associations and Demographics

Pyoderma gangrenosum is most strongly associated with inflammatory bowel disease (particularly ulcerative colitis, occurring in 0.6-2.1% of patients), hematological malignancies, and inflammatory arthritides, with 50-70% of all cases linked to underlying systemic disorders. 1, 2

Primary Associated Systemic Diseases

Gastrointestinal Disorders

• Inflammatory bowel disease represents the most common association, with ulcerative colitis showing higher frequency than Crohn's disease 1, 2
• The prevalence in UC patients ranges from 0.6-2.1%, while gastrointestinal disease overall was found in 29.2% of PG patients in clinical series 1, 3
• IBD activity may parallel PG lesions or run an independent course, meaning PG can flare independently of bowel disease activity 2

Hematological Disorders

• Hematologic malignancies occur in approximately 25% of PG cases, including myelodysplastic syndrome, acute myeloid leukemia, and paraproteinaemias 4, 3, 5
• Myeloproliferative disorders should be specifically screened for during workup 6

Rheumatologic Conditions

• Inflammatory arthritides including rheumatoid arthritis and spondyloarthropathies (particularly ankylosing spondylitis) are recognized associations 2, 7, 5
• Autoimmune inflammatory diseases were present in 12% of patients in one series 3

Other Associations

• Solid tumors occur in approximately 8.3% of cases 3
• Hidradenitis suppurativa shows association with PG, warranting screening in HS patients 1

Demographic Characteristics

Gender Distribution

• Female predominance is consistently observed with a female-to-male ratio of approximately 3.8:1 3
• However, genital PG specifically shows male predominance (76.9% male) 4

Age Range

• PG affects a wide age range from 17 to 89 years, with a mean age of approximately 58 years 3
• The condition can occur in young adults through elderly patients 4, 3

Incidence

• Overall incidence is 3-10 cases per million population, though this may be underestimated due to under-recognition and misdiagnosis 7

Clinical Pattern Considerations

Anatomic Distribution

• Lower extremities are affected in approximately 70-79% of cases, particularly the shins 1, 4, 3
• Peristomal areas are common sites, especially in IBD patients with ostomies 1, 8
• Genital involvement is rare but can occur, with genitalia-localized PG tending to occur without systemic complications in 8 of 9 cases 4

Pathergy Phenomenon

• Trauma triggers lesion development in 20-30% of cases, explaining post-surgical and peristomal occurrences 2
• This pathergy response is critical to recognize, as surgical debridement during active disease should be avoided 6

Screening Implications

When PG is Diagnosed

• Screen for inflammatory bowel disease through colonoscopy and inflammatory markers 2, 6
• Obtain complete blood count with differential to evaluate for hematologic malignancies 6
• Assess for inflammatory arthritides through rheumatologic evaluation if joint symptoms present 2
• Consider screening for hidradenitis suppurativa in appropriate patients 1

Important Caveat

• 50-70% of cases have underlying systemic disease, but some cases may precede the diagnosis of the underlying condition, particularly IBD, making longitudinal monitoring essential even if initial workup is negative 2
• Conversely, 25-50% of PG cases are idiopathic without identifiable systemic association 2, 5

Recurrence Risk

• High recurrence rate exceeding 25% following successful treatment, with recurrences often occurring at the same anatomic location as the initial episode 2, 6, 3