Acanthosis nigricans is a pigmented skin lesion commonly present in the axilla which is a phenotypic marker for an insulin-receptor abnormality as well as a marker for adenocarcinoma, most commonly of gastric origin.

Paget Disease (Osteitis Deformans) 

This unique bone disease is characterized by repetitive episodes of exaggerated, regional osteoclastic activity (osteolytic stage), followed by exuberant bone formation (mixed osteoclastic-osteoblastic stage), and finally by exhaustion of cellular activity (osteosclerotic stage). The net effect of this process is a gain in bone mass; however, the newly formed bone is disordered and lacks strength. Paget disease usually does not occur until mid-adulthood but becomes progressively more common thereafter. The pathognomonic histologic feature is a mosaic pattern of lamellar bone (likened to a jigsaw puzzle) due to prominent cement lines that haphazardly fuse units of lamellar bone. (Fig. 12-5) The axial skeleton and proximal femur are involved in the majority of cases. In patients with extensive disease, hypervascularity of the marrow spaces can result in high-output congestive heart failure. Cranial nerves impingement also occurs and can lead to head ache and auditory disturbances. Rarely Paget disease is complicated by bone sarcoma (usually osteogenic). 

Acne vulgaris is a chronic inflammatory disorder usually present in the late teenage years characterized by comedones, papules, nodules, and cysts.
 - subdivided into obstructive type with closed comedones (whiteheads) and open comedones (blackheads) and the inflammatory type consisting of papules, pustules, nodules, cysts and scars.
 - pathogenesis of inflammatory acne relates to blockage of the hair follicle with keratin and sebaceous secretions, which are acted upon by Propionibacterium acnes (anaerobe) that causes the release of irritating fatty acids resulting in an inflammatory response.
 - pathogenesis of the obstructive type (comedones) is related to plugging of the outlet of a hair follicle by keratin debris.
 - chocolate, shellfish, nuts iodized salt do not aggravate acne.
 - obstructive type is best treated with benzoyl peroxide and triretnoin (vitamin A acid)
 - treatment of inflammatory type is the above plus antibiotics (topical and/or systemic; erythromycin, tetracycline, clindamycin).

Plasma Cell Pathology

A. Multiple myeloma

1. Plasma cell neoplasm that results in the proliferation of monoclonal plasma cells. These tumor cells produce nonfunctional immunoglobulins.

2. Laboratory findings include:

a. Monoclonal IgG spike.

b. Bence-Jones proteins found in urine.

3. Radiographic findings: characteristic “punched-out” radiolucencies in bones.

Seborrheic dermatitis is a scaly dermatitis on the scalp (dandruff) and face.
 - due to Pitysporium species
 - can be seen in AIDS as an opportunistic infection

Pulmonary Hypertension 

Sustained elevation of mean pulmonary arterial pressure.

Pathogenesis 
Elevated pressure, through endothelial cell dysfunction, produces structural changes in the pulmonary vasculature. These changes ultimately decrease pulmonary blood flow and stress the heart to the point of failure. Based on etiology, pulmonary hypertension is divided into two categories.

Primary (idiopathic): The cause is unknown.
Secondary: The hypertension is secondary to a variety of conditions which increase pulmonary blood flow or increase resistance to blood flow. Example: Interstitial fibrosis.
Pathology 
The changes involve large and small pulmonary blood vessels and range from mild to severe. The major changes include atherosclerosis, striking medial hypertrophy and intimal fibrosis of small arteries and arterioles, and plexogenic arteriopathy. Refer to Figure 15-7 in your textbook.

Pathophysiology 
Dyspnea and fatigue eventually give way to irreversible respiratory insufficiency, cyanosis and cor pulmonale.