Current studies indicate that HS is more common in females than males, at a rate of approximately 3:1. 1 Disease prevalence has also been determined to be higher in African American individuals, as well as obese patients and those who smoke. 1,2 Further studies are necessary to more fully define the demographics and epidemiology of the disease on a broader scale.
Although a complete understanding of the disease process has yet to be determined, HS is complex, likely with both genetic and environmental factors involved in its development. Interestingly, it has been found that many diseases are co-associated with HS, although a common mechanism for the relationship has not been determined. These associations are useful for holistic patient care, education, and management of HS.1
Frequently observed conditions with HS include metabolic syndrome (elevated cholesterol and blood lipids, diabetes, and obesity), cardiovascular disease (CVD), autoimmune thyroid disease, arthropathies (joint disease), acne and other inflammatory skin conditions, squamous cell carcinoma, polycystic ovary syndrome (PCOS), pyoderma gangrenosum, and inflammatory bowel disease. 3-7 The identification of many associated diseases indicates the systemic effects of HS, a condition that is likely not confined purely to the skin. 7
Metabolic Syndrome is defined as a group of risk factors including obesity, dyslipidemia, hyperglycemia (diabetes), and hypertension (high blood pressure). Metabolic syndrome increases the risk of CVD, which includes but is not limited to heart attacks, arrhythmias, and strokes 5. Recent studies have indicated that a significantly higher proportion of patients with HS have metabolic syndrome compared to controls, particularly an increased incidence of obesity, hypertriglyceridemia, and glucose intolerance. 5,8 At this time, it is uncertain whether or not treatment for metabolic syndrome will improve outcomes of HS, although knowledge of the association is clinically valuable for appropriate patient care. 5,6
Cardiovascular Disease (CVD) is a concerning condition. As described above, patients with HS have an increased risk for CVD. 5 Additionally, a study of 5,964 patients provided evidence that the risk of cardiovascular associated death was higher in HS patients. This study also determined an increased risk of all-cause mortality (risk of death) in HS patients. 9 This information is incredibly valuable as it provides both patients and physicians with a more comprehensive understanding of the relationship between CVD with HS. This knowledge should also prompt physicians to carry out appropriate screening and evaluation for management of CVD risk factors in HS patients.
Thyroid disease has been correlated with the presence of HS. 10,11 In fact, a recent case study described the coexistence of Hashimoto’s thyroiditis (an autoimmune thyroid disease leading to low thyroid hormone levels) with HS, a field of active research. A recent study recommended the evaluation of thyroid function in patients with HS due to the relationship between the two diseases. 12 This association has provided valuable information for comprehensive patient care.
Arthropathy is a term describing joint disorders, such as psoriatic and rheumatoid arthritis. Both are defined as chronic autoimmune conditions that cause systemic and joint inflammation, particularly of large joints such as the knees and wrists. Both have been associated with HS. 10 Additionally, spondyloarthropathy is a joint disease of the spine, and the non-genetic (HLA-B27 negative) type of this disease has been associated with HS. 11 Systemic inflammation may be the connecting factor between these arthropathies and HS, although further studies are necessary. 10
PCOS is a disorder characterized classically by an imbalance of female sex hormones, growths on the ovaries, and ovarian dysfunction. In a classic patient presentation, PCOS leads to irregular period cycles and increases the risk of acne and facial hair. 13 HS, too, has a predilection for women, and hormonal imbalance has been suggested as a potential source of development for this disease as well. 1,13
Acne and other chronic suppurative (pus-forming) skin diseases were some of the first conditions to be associated with HS. In particular, relationships exist between HS and acne conglobata, pilonidal disease, and dissecting cellulitis. 7 Each of the previously listed diseases is a type of inflammatory, chronic, suppurative skin disorder, similar to HS. Acne conglobata is a severe, inflammatory form of acne that may cause the development of deep, draining sinus tracts. 14 Pilonidal disease involves the formation of an abscess near the coccyx (tailbone). This abscess may be painful and may lead to the development of an infected sinus tract. 15 Dissecting cellulitis is a chronic disease, often of the scalp, involving deep nodules and inflamed abscesses that may expand. Similarly to HS, the etiology is unknown, although the disease is likely immune and inflammatory mediated. 14
Squamous cell carcinoma is the second most common type of skin cancer, and is considered the most severe complication of HS, with a prevalence of 0.5-4.6% in this patient population. 10,16 The chronic inflammation of draining HS lesions may lead to skin changes at the cellular level, eventually resulting in this form of skin cancer. It is important that dermatologists are aware of this risk and biopsy any concerning lesions, as early diagnosis can be lifesaving. 7
Inflammatory Bowel Disease is defined as a group of chronic inflammatory gastrointestinal conditions, including ulcerative colitis and Crohn’s disease. Symptoms classically include abdominal pain, bloody stools, diarrhea, and may also include a wide variety of associated extraintestinal symptoms, such as HS. Inflammatory bowel disease, particularly Crohn’s disease, has been associated with HS. 4
Pyoderma gangrenosum (PG) is a rare inflammatory disease often associated with systemic diseases. PG is characterized by the formation of non-infectious, ulcerative skin lesions often observed on the lower limbs. 3 PG and HS have also associated in a variety of studies, as well as independently in case reports. 10 This relationship is perhaps representative of the prolonged systemic inflammation of HS. 3
This list is an example of conditions commonly associated with HS, although other relationships exist, including rare genetic keratin disorders and lymphoma. 3,16,17 As research continues, additional associations will likely to be illuminated, along with a more complete understanding of the cause and pathogenesis of HS. The field of HS is an exciting and rapidly developing topic of research, with invaluable results for patients dealing with the distressing disease, and physicians managing patients with HS.