The correct answer is "Vinblastine-induced neuropathy." 

This is the most likely explanation for this patient's peripheral neuropathy, as the patient is described as being healthy aside from Hodgkin's lymphoma, and on no medications aside from his chemotherapy regimen. As a result, diabetic neuropathy and selective serotonin reuptake inhibitor discontinuation syndrome can each be ruled out as etiologies. Similarly, given that he is otherwise healthy and not complaining of any additional neurological symptoms (and given that he is young and actively receiving chemotherapy) it is unlikely that he is experiencing posterior spinal cord degeneration. 

Thus, in a young patient with lymphoma who is receiving chemotherapy and experiencing peripheral neuropathy, the most likely etiology is one of the chemotherapy medications that he is receiving. In this patient's case, he is receiving doxorubicin, bleomycin, vinblastine, and dacarbazine. Of these medications, vinblastine is the most strongly associated with peripheral neuropathy, as this is a fairly common side effect of vinblastine and other agents in the same class (vinca alkaloids). As such, vinblastine-induced neuropathy is the most likely etiology.

The correct answer is "PET-CT." This is the correct answer because a PET-CT shows not only spatial information from the serial slices taken on CT imaging, which would include the size and location of any potential tumor, scarring, or nodal involvement, but also the FDG-avidity or uptake of the contents of the image, which would help correlate the spatial findings with possible disease activity. Nodules observed on a CT scan can be non-descript, ranging from malignant, to indeterminate, to benign (which may still be infectious or inflammatory). The addition of PET to a CT allows the observer to see which nodules, nodes, or lesions are more likely to be indicative of disease burden, as tumors and infections will have greater FDG uptake since they are more metabolically active than surrounding tissues. 

MRI is not typically used to assess treatment in lung cancer as CT coupled with PET is more commonly used. X-ray does not provide enough resolution to adequately assess response to cancer treatment. Pulmonary function tests, while a useful measure of lung functionality, do not give a specific picture of the lung cancer burden and as such are not the best treatment response assessment tool.

The correct answer is "MRI Head." This is the correct answer because in evaluating brain parenchyma, which is relatively soft tissue, MRI provides the greatest degree of spatial resolution, which would best allow assessment of any residual, recurrent, or new tumor burden within the brain. CT imaging is commonly used to assess the brain when evaluating for bleeds or fractures, among other conditions, as it is far more expedient than MRI. However, it does not visualize the soft tissue of the brain parenchyma as well as MRI, and treatment response MRI scans are often not emergent, and therefore MRI would be preferred. PET-CT, while often highly useful in oncologic assessments is of limited value in evaluating the brain for cancer response, because the entire brain is highly metabolically active in nearly all patients, and therefore the entire brain typically has a great deal of FDG uptake uniformly, limiting the value of the scan.

The priority for this client is to ensure a patent airway by placing him the Fowler's or semi upright seated position. Giving oxygen is warranted but will be given after the client is positioned correctly. ABG's would be helpful in this situation but it not the priority. Auscultation of breath sounds and assessment of mental status are not indicated.

The final stage of a pertussis infection is known as the convalescent phase. This occurs for 2-6 weeks, after the paroxysmal stage of the disease. During this time coughing decreases, and paroxysms are less severe. The infected individual may experience increased susceptibility to upper and lower respiratory conditions for as much as 6 months after resolution of the infection.

Whooping cough, a condition that results in severe paroxysmal coughing fits followed by a long wheezing inspiratory gasp (the "whoop") is caused by the bacteria Bordetella pertussis. Haemophilus influenzae and Klebsiella pneumoniae both commonly cause pneumonia, and RSV is a virus that is frequently implicated in lower respiratory infections of infants and children.

After the catarrhal stage, an individual with pertussis will progress into the paroxysmal stage. It's during this stage that they will experience uncontrollable fits of 5-15 forceful coughs, followed by a "whoop" or gasp as they struggle to inhale. The force of these coughs can be such that they can result in vomiting, epistaxis, subconjunctival hemorrhage, or even broken ribs. 

The incubation period for pertussis, also known as the catarrhal stage, can last as little as 4 days or as long as 42 days, but a typical period is 1-3 weeks. During this stage the disease looks like a regular upper respiratory infection, with sneezing, mild cough, and runny nose. The infected individual is highly infectious at this time, with bacteria spread by airborne droplets after sneezing or cough. 

The correct answer is "Sarcoidosis." Sarcoidosis is the correct answer as this inflammatory condition is frequently found in African-American women in their 40's who present with fatigue and shortness of breath among other symptoms, who also have erythema nodosum on the lower extremities, and have bilateral hilar infiltrates on chest x-ray. This constellation of findings is highly suggestive of sarcoidosis. Sarcoidosis results in the formation of numerous non-necrotizing granulomas, most commonly found in the lungs, that can play a role in the symptoms experienced by these patients. Other findings suggestive of sarcoidosis include elevated serum calcium levels with normal serum PTH levels.

Tuberculosis can present in a similar manner to sarcoidosis, however given the patient's suburban living environment, lack of a travel history, and lack of healthcare exposure, the likelihood of being exposed to tuberculosis is very low, making sarcoidosis a more likely etiology.

While lung cancer can present as shortness of breath with hilar infiltration in chest x-ray, in a relatively young otherwise healthy patient who also has erythema nodosum and in whom the hilar infiltrates are bilateral, sarcoidosis would be a more likely etiology.

The patient does not have any findings consistent with meningitis (leg rash in meningitis is petechial, not erythema nodosum) or pharyngitis.

Incidence of asthma is lower in populations exposed to an abundance of microbes from a young age. The "hygiene hypothesis" suggests that early immune stimulation by multiple forms of infectious agents may push a Th1 phenotype, reducing the Th2 (allergic) response.