Nodular prurigo or Prurigo nodularis is a very itchy dermatosis of unknown etiology. It is characterized by:
* Firm nodules, 1–3 cm in diameter, often with a verrucous surface.
* Crusting and scaling may cover recently scratched lesions.
* Older lesions may be darker or paler than surrounding skin.
* Distribution is usually bilateral symmetrical. The lumps usually start on the forearms and legs, and are worse on the outer aspects. The trunk, face and even palms can also be affected.
* Sometimes, the nodules are most obvious on the cape area (neck, shoulders and upper arms).
* The nodules are grouped and numerous but may vary in number from 2–200.
* New nodules appear from time to time, but existing nodules may regress spontaneously to leave scars.
* PN Can occur at all ages but mainly in adults aged 20–60 years.
* Both sexes are equally affected.
* The course often is long and can lead to significant stress and depression.

Etiology
* The cause is unknown. It is uncertain whether scratching leads to the lumps, or if the lumps appear before they are scratched.
* Up to 80% of patients have a personal or family history of atopic dermatitis, asthma or hay fever (compared to about 25% of the normal population).
* PN may start as an insect bite reaction or another form of dermatitis.
* PN has been associated with internal or cutaneous disease including:
1. Iron deficiency anemia
2. Chronic renal failure
3. Gluten enteropathy
4. HIV infection and many other diverse conditions.
5. Brachioradial pruritus (due to compression or traction of spinal nerves).

Investigations
1. Skin biopsy: the diagnosis of PN is primarily clinical and may be confirmed by skin biopsy which shows enormously thickened skin that may appear quite abnormal, sometimes resembling squamous cell skin cancer. The nerve fibers and nerve endings in the skin are markedly increased in size.
2. Direct immunofluorescence is usually negative.
3. Other investigations are important to be arranged to identify underlying diseases that are associated with nodular prurigo such as: CBC, LFTs, RFTs and TFTs.

Treatment
PN is one of the resistant dermatoses to be amenable to treatment. Local treatments tried include:
1. Emollients applied liberally and frequently to cool and soothe itchy skin – menthol or phenol may be added. Oral antihistamines may be given at night to reduce itch and allow sleep.
2. Ultrapotent topical steroids under occlusion. Corticosteroid injections (triamcinolone acetonide 10 – 40 mg /ml) into thicker nodules.
3. Coal tar ointment as steroid alternative.
4. Calcipotriol ointment may be more effective than topical steroids in some cases.
5. Capsaicin cream, which induces itching and burning until eventually the itch stops completely – it requires repeated applications four to six times daily.
5. Cryotherapy, which may shrink the nodules and reduce their itch.
6. Pulsed dye laser, which may reduce the vascularity of individual lesions.

Systemic treatments: may be helpful for more severe disease. Combination treatment is frequently recommended.
1. Phototherapy (UVB and PUVA)
2. Tricyclic anti-depressants such as amitriptyline or doxepin
3. Anticonvulsants used for neuropathic pain and itch, such as gabapentin or pregabalin
4. Naltrexone, an opiate antagonist has been reported to reduce itching in some subjects.
5. Oral steroids
6. Methotrexate
7. Thalidomide (reserved for very severe cases)
8. Ciclosporin, which may reduce the lumps and the itching but its use is limited by side effects.
9. Systemic retinoids such as acitretin or isotretinoin, which may shrink the nodules and reduce the severity of the itch.

Pigmented papillae of the tongue (PFPT) is a benign condition characterized by well-circumscribed hyperpigmentation confined solely to fungiform papillae. Lesions are generally asymptomatic.

PFPT is generally considered as a common finding in African American individuals, in Australian aborigines and Indians. It is considered rare in people with light skin.

The pathogenesis and the reason for the abnormalities being limited to the fungiform papillae remains unknown. It could be considered a benign variant of oral hyperpigmentation seen in high phototypes and would denote an active pigmentation system in an area where it is generally inactive.

The histological features of pigmented fungiform papillae include numerous melanophages in the lamina propria of the papillae with lack of inflammatory infiltrates. The pigment located within the melanophages stains positive for melanin with Fontana-Masson and negative for iron with Prussian blue.

Differential diagnosis include other causes of pigmentation of the oral mucosa such as hemochromatosis, pernicious anemia, amalgam tattoo, Peutz-Jeghers syndrome, Addison’s disease, von Recklinghausen syndrome and melanocytic nevus.
However, a clear diagnosis can be reached in all those disorders on the basis either of the distribution and clinical characteristics of the pigmentation or the accompanying manifestations.

No treatment is required as the condition may be considered as normal variant.

* A rare form of intraepithelial neoplasia (a pre-cancerous dermatosis).
* In females it is vulvar intraepithelial neoplasis (VIN) and in males it is a type of penile intraepithelial neoplasia.
* HPV has been closely linked to BP as a cause.
* Most cases of BP are benign, however, a small percentage may transform into invasive squamous cell carcinoma (penile or vulvar cancer).
* Sexually active people may be at risk of getting BP, it is most often passed through direct skin-to-skin sexual contact. So partners of patients with BP should be screened for other forms of intraepithelial neoplasia (cervical, penile, vulvar and anal).
* Men and women are equally at risk and the peak incidence is in sexually active persons under 30 years of age.
* It usually presents as small red, brown or flesh-colored flat or warty papules appear most commonly on the shaft of the penis or labia of females. The lesions may also involve other parts of the genitals as well as in and around the anus. The condition is usually asymptomatic but occasionally lesions may become inflamed, itchy and painful.
* BP tends to spontaneously disappear within several months and if a woman is pregnant when it is diagnosed it will often disappear after delivery. If it is persistent this is an indication for active treatment because of the chance of developing skin cancer.
* Once infected with HPV you may become a lifelong carrier of the virus and recurrence of BP or other intraepithelial cancers in the genital area is possible.
* Diagnosis of BP is made by its typical clinical appearance, especially with the aid of dermoscopy, or by skin biopsy. SCC in situ pathology is diagnostic on skin biopsy.
* Treatment: because it usually runs a benign course with many cases spontaneously regressing, treatment is often unnecessary. Lesions should be re-examined every 3 to 6 months so that any changes may be picked up early.
If the lesions are persistent, treatment of BP is the same as for genital warts i.e. usually destruction of the lesions via several medical and/or surgical procedures. Regular checks are necessary after treatment to ensure the condition has completely resolved.
Summary: BP is wart clinically and carcinoma in situ histopathologically!

Lupus vulgaris
* A common form of cutaneous tuberculosis although the cut. Tb is rare.
* The skin is involved by endogenous spread from an old reactivated Tb focus in the lungs or through lymphatics from a Tb cervical lymph node.
* Rarely LV is due to exogenous reinfection.
* LV is a form of postprimary Tb that occurs in a sensitized person.
* Any age can be involved by LV and it is more common in females.
* > 80% of the cases affect the head and neck region especially the nose, ears and the scalp. The trunk and extremities are involved in < 20% of the cases.
* Asymptomatic, well-defined, reddish brown, irregular plaques with characteristically soft consistency having a smooth or slightly scaly surface with deep-seated nodules. Usually there is only one or few lesions.
* Diascopy reveals an apple-jelly colored (yellowish-brown) infiltrative nodules which is a characteristic of LV.
* The lesions tend to extend peripherally and heal with atrophic “unhealthy” scarring at the center. However, new brownish infiltrates or nodules may appear within the atrophic areas which is another characteristic feature of LV.
Variants of LV:
1. Hypertrophic LV: Soft tumorous nodules.
2. Hyperkeratotic (Warty) LV: Verrocous surface.
3. Ulcerative LV: Punched-out superficial ulcers surrounded by soft brownish infiltrates.
4. Mutilating LV: involvement of underlying cartilages (but not bones) resulting in mutilation especially of the nose and ears with prominent scarring.
* The course of LV: a slow, progressive, prolonged course which may be life-long if left untreated. Rarely, SCC may complicate LV.
Differential diagnosis:
1. DLE
2. Chronic lupoid leishmaniasis
3. Lepromatous leprosy
4. Tertiary syphilis
5. SCC

Don’t forget Darier’s disease in spite of its rarity !
1. Autosomal dominant inheritance.
2. Usual onset before 30 years.
3. Dirty warty papules mainly in seborrheic areas. The skin may have coarse sandpaper texture.
4. Photoexacerbation of the rash is common.
5. Palmoplanter pits.
6. Characteristic V-shaped nicks at the free edge of the nails.
7. Keratosis follicularis (Acrokeratosis verruciformis) on hands and feet.
8. Red mucous membranes and occasinally have cobblestone appearance.
9. A characteristic “focal acantholytic dyskeratosis” picture on histopathology.
10. Retinoids (Acitretin/ Isotretinoin) are usually effective in severe cases.

What are the therapeutic options of necrobiosis lipoidica ?
1. Corticosteroids: Superpotent topical corticosteroids with occlusion, intralesional injections of triamcinolone suspension into the the active advancing edges but not the waxy yellow center (risk of ulceration) and systemic steroids in selected cases.
2. Topical calcineurin inhibitors.
3. Pharmalogical agents improving the blood circulation: low-dose aspirin, nicotinamide, pentoxifylline, and dipyridamole.
4. Phototherapy (PUVA and UVA1).
5. Oral immunomodulators (Antimalarial drugs and thalidomide).
6. Cyclosporin A in selected cases.
7. In refractory cases: TNF inhibitors (Infliximab and Etanercept): systemically or intralesionally.
8. Ulcerative cases: Surgical excision and grafting.