History

Fact Explanation
Rash Prurigo refers to intensely itchy spots. This can occur with many other disease conditions. But the exact pathophysiology is not known. Lesions of the Prurigo simplex variant are dome-shaped bumps (papules). They are intensely itchy and symmetrically distributed. These bumps are either stable or increasing in number. But at times there are some blisters as well. The rash is more common on the outer surface of the limbs and buttocks but can occur elsewhere as well. The face, palms of the hands, and plantar surfaces of the feet are usually not affected. There is no involvement of the mucous membranes. [1,2,3,4,5]
Ulcers Prurigo, specially nodular variant often results in ulcerations. This may be prone to secondary bacterial infections characterized by crusting. [1,2,3]
Dark spots The spots are replaced by hyperpigmentation eventually, specially in variants like Prurigo pigmentosa and nodular prurigo. [1,3,4,5]
History of similar events Patients usually give a long-standing history of severe, unremitting pruritus. [1,5]
Associations In some people, prurigo is associated with another skin condition or health problem. These include atopic eczema, discoid eczema, papular urticarial, iron deficiency, thyroid disease, HIV, chronic renal failure or polycythaemia rubra vera etc. [1,2,3,5]
References
  1. IIJIMA S. Prurigo nodularis. Tohoku J Exp Med [online] 1951 Apr, 54(1):73-80 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/14846088
  2. LIN SH, HO JC, CHENG YW, HUANG PH, WANG CY. Prurigo pigmentosa: a clinical and histopathologic study of 11 cases. Chang Gung Med J [online] 2010 Mar-Apr, 33(2):157-63 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/20438668
  3. WEISSHAAR E, STäNDER S. Prurigo nodularis in hepatitis C infection: result of an occupational disease? Acta Derm Venereol [online] 2012 Sep, 92(5):532-3 [viewed 26 August 2014] Available from: doi:10.2340/00015555-1209
  4. BOER A, ASGARI M. Prurigo pigmentosa: an underdiagnosed disease? Indian J Dermatol Venereol Leprol [online] 2006 Nov-Dec, 72(6):405-9 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/17179613
  5. DALDON PE, PASCINI M, CORREA M. Case for diagnosis. Actinic prurigo. An Bras Dermatol [online] 2010 Sep-Oct, 85(5):733-5 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/21152806

Examination

Fact Explanation
Papules Lesions of the Prurigo simplex variant are dome-shaped papules. They are symmetrically distributed all over the body, specially on the limbs and buttock. [1,2]
Nodules Nodular prurigo presents with sharply demarcated, tough, mildly erythematous nodules which are symmetrically distributed specially on the outer surfaces of the limbs and buttocks. Face, palms of the hands, and plantar surfaces of the feet are often spared. However intense scratching may result in the distortion of the primary skin lesion. [1,2,3,4]
Ulcerations As patients often scratch intensely gray or purple and sometimes verruciform keratotic areas, excoriations and crater-like ulcerations may occur. These ulcerations are covered by and hemorrhagic crusts initially. [1,3,5]
Bacterial infections The ulcers may be secondarily infected by bacterias. This results in forming a yellowish crust over the lesion. [2,3,5]
Butterfly sign Typically there is an area of skin that is unaffected which the patient cannot reach, such as the middle of the back. This characteristic feature of prurigo nodularis is referred to as the “butterfly sign”. [1,3,5]
Depigmentation Following the healing, the rash will be replaced by post inflammatory hyperpigmentation. Rarely hypopigmentations may also occurs. The skin between individual lesions is generally normal,but there is sometimes xerosis cutis. [2,3,4,5]
References
  1. DALDON PE, PASCINI M, CORREA M. Case for diagnosis. Actinic prurigo. An Bras Dermatol [online] 2010 Sep-Oct, 85(5):733-5 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/21152806
  2. WEISSHAAR E, STäNDER S. Prurigo nodularis in hepatitis C infection: result of an occupational disease? Acta Derm Venereol [online] 2012 Sep, 92(5):532-3 [viewed 26 August 2014] Available from: doi:10.2340/00015555-1209
  3. BOER A, ASGARI M. Prurigo pigmentosa: an underdiagnosed disease? Indian J Dermatol Venereol Leprol [online] 2006 Nov-Dec, 72(6):405-9 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/17179613
  4. IIJIMA S. Prurigo nodularis. Tohoku J Exp Med [online] 1951 Apr, 54(1):73-80 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/14846088
  5. LIN SH, HO JC, CHENG YW, HUANG PH, WANG CY. Prurigo pigmentosa: a clinical and histopathologic study of 11 cases. Chang Gung Med J [online] 2010 Mar-Apr, 33(2):157-63 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/20438668

Differential Diagnoses

Fact Explanation
Keratoacanthoma Keratoacanthoma is a benign epithelial neoplasm which originates in the epithelium of the hair follicle above the sebaceous glands. Sometimes it is considered as a form of squamous cell carcinoma. Keratoacanthoma grows rapidly over a few weeks to months, followed by a slow spontaneous resolution over 4 months to 1 year. The lesion mostly occurs on sun-exposed areas such as face, neck, and dorsum of hands and forearms. They are usually solitary and begin as firm, round, skin-coloured or reddish papule. This initial papule rapidly progresses to a dome-shaped nodules with a smooth shiny surface. With time, the papule grows rapidly, reaching a large size within days or weeks. And then it begin to necrose resulting a central crater of ulceration. [1]
Lichen Simplex Chronicus Lichen simplex chronicus (neurodermatitis) is a localized area of chronic, lichenified eczema/dermatitis. Patient usually has an underlying skin condition that results in repetitive scratching or rubbing. Though the exact pathophysiology is unknown, it makes the affected skin markedly thickened. There may be several affected areas in the body. The site are usually those which can be easily reachable such as scalp, extensor forearms, nape of neck and elbows, vulva and scrotum, upper medial thighs, knees, lower legs, and ankles. A solitary plaque of lichen simplex is circumscribed, somewhat linear or oval in shape. Surface is dry and hard. The area is intensely itchy. This is usually due to the underlying skin conditions. Rarely psychological issues may also involve. Itching is more intense at rest than when the patient is active. So, it is more common at night. Patient may complain of sleep disturbances. Itching may be habitual as well. [2]
Milker's Nodules Milker's nodule is an infection of the skin caused by a virus that infects the teats of cows. Milker's nodule is caused by a parapoxvirus. After an incubation period of 5-14 days small, red, raised, flat-topped spots develop. Within a week they appear as red-blue, firm, slightly tender blisters or nodules (lumps), usually between 2 and 5 in number although they may be solitary or more numerous. The nodules are usually on the hands, particularly the fingers, but occasionally the face. The top of the nodules often develops a greyish skin and a small crust. [3]
Insect Bites Insect bites and stings can be simply divided into 2 groups: venomous and non-venomous. For most people, insect bites or stings cause a mild reaction. Venomous stings usually cause a stinging sensation or pain with redness and swelling of the area. Itch is usually not a concern. In some people who are sensitive to insect venom, a sting may cause a severe allergic reaction known as anaphylaxis. This results in facial swelling, difficultly breathing and an itchy rash (urticaria) over most of the body. This can be life-threatening so immediate medical attention and treatment needs to be sought. [4]
References
  1. SAZAFI MS, SALINA H, ASMA A, MASIR N, PRIMUHARSA PUTRA SH. Keratoacanthoma: an unusual nasal mass. Acta Otorhinolaryngol Ital [online] 2013 Dec, 33(6):428-30 [viewed 18 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/24376301
  2. PRAJAPATI V, BARANKIN B. Dermacase. Lichen simplex chronicus. Can Fam Physician [online] 2008 Oct, 54(10):1391-3 [viewed 11 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/18854464
  3. SIMMONS JF, HAFERNICK AC. Painless, red nodule on the finger of a veterinary student. Am Fam Physician [online] 2012 Jul 1, 86(1):77-8 [viewed 02 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/22962916
  4. SINGH S, MANN BK. Insect bite reactions. Indian J Dermatol Venereol Leprol [online] 2013 Mar-Apr, 79(2):151-64 [viewed 21 August 2014] Available from: doi:10.4103/0378-6323.107629

Investigations - for Diagnosis

Fact Explanation
Full blood count This is important as an initial assessment of hematologic disease that can result in similar clinical picture. [1,2,3]
Liver function test This is done to exclude underlying hepatic disease that result in similar dermatological features. [2,3]
Blood urea nitrogen (BUN) This is done to exclude the dermatological manifestations related to uremia and renal transplantation. [2,3,5]
Skin biopsy Skin biopsy is often performed to look for specific features of dermatitis herpetiformis, which are diagnostic of that condition. Direct immunofluorescence is also diagnostic for dermatitis herpetiformis. The histology of other forms of prurigo may be nonspecific, or show hyperkeratosis (scale), acanthosis (skin thickening) and inflammatory infiltrate (lymphocytes in the dermis). [1,3,5]
References
  1. WEISSHAAR E, STäNDER S. Prurigo nodularis in hepatitis C infection: result of an occupational disease? Acta Derm Venereol [online] 2012 Sep, 92(5):532-3 [viewed 26 August 2014] Available from: doi:10.2340/00015555-1209
  2. IIJIMA S. Prurigo nodularis. Tohoku J Exp Med [online] 1951 Apr, 54(1):73-80 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/14846088
  3. DALDON PE, PASCINI M, CORREA M. Case for diagnosis. Actinic prurigo. An Bras Dermatol [online] 2010 Sep-Oct, 85(5):733-5 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/21152806
  4. LIN SH, HO JC, CHENG YW, HUANG PH, WANG CY. Prurigo pigmentosa: a clinical and histopathologic study of 11 cases. Chang Gung Med J [online] 2010 Mar-Apr, 33(2):157-63 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/20438668
  5. BOER A, ASGARI M. Prurigo pigmentosa: an underdiagnosed disease? Indian J Dermatol Venereol Leprol [online] 2006 Nov-Dec, 72(6):405-9 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/17179613

Management - Specific Treatments

Fact Explanation
Corticosteroids Topical, oral, and intralesional corticosteroids decrease the inflammation and itching. Application of topical corticosteroids such as mometasone furoate or methylprednisolone aceponate should be done under occlusion. Intralesional application of corticosteroids such as triamcinolone acetonide suspension is also effective. [1,2,3,4,5]
Antihistamines Chlorpheniramine may improve pruritus and reduce sleep disturbance. [3,4,7]
Antibiotics Topical or systemic antibiotics are only used in case of secondary bacterial infection. [1,3,5]
Phototherapy Ultraviolet light induces anti-inflammatory and immunosuppressive factors. It also has antiproliferative effects. [3,5,6]
immune suppressive agents More severe disease may be treated with immune suppressive agents such as Methotrexate, Azathioprine and Ciclosporin. [3,4,7]
Tricyclic antidepressants Tricyclic antidepressants such as amitriptyline, anticonvulsants such as gabapentin, pregabalin or sodium valproate and opiate antagonists such as naltrexone are used to reduce severe itching. Other topical medications known to decrease pruritus include doxepin cream and capsaicin cream. [1.3.6.7]
Cryotharapy Liquid nitrogen is used depending on the size of the lesions. The therapy varies from 10-30 seconds with two to four “freeze-thaw cycles.” It can take up to four weeks until the treated nodules heal. Residual scarring can occur. After cryosurgery, patients can be pruritus- free for up to three months. [1,2,3,4]
References
  1. WEISSHAAR E, STäNDER S. Prurigo nodularis in hepatitis C infection: result of an occupational disease? Acta Derm Venereol [online] 2012 Sep, 92(5):532-3 [viewed 26 August 2014] Available from: doi:10.2340/00015555-1209
  2. BARBER HW. Case of Prurigo Nodularis. Proc R Soc Med [online] 1924, 17(Dermatol Sect):3-5 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/19983558
  3. Prurigo. Proc R Soc Med [online] 1933 Apr, 26(6):750 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/19989263
  4. IIJIMA S. Prurigo nodularis. Tohoku J Exp Med [online] 1951 Apr, 54(1):73-80 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/14846088
  5. BOER A, ASGARI M. Prurigo pigmentosa: an underdiagnosed disease? Indian J Dermatol Venereol Leprol [online] 2006 Nov-Dec, 72(6):405-9 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/17179613
  6. LIN SH, HO JC, CHENG YW, HUANG PH, WANG CY. Prurigo pigmentosa: a clinical and histopathologic study of 11 cases. Chang Gung Med J [online] 2010 Mar-Apr, 33(2):157-63 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/20438668
  7. DALDON PE, PASCINI M, CORREA M. Case for diagnosis. Actinic prurigo. An Bras Dermatol [online] 2010 Sep-Oct, 85(5):733-5 [viewed 26 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/21152806